P-K MODU-FIRE FORCED-DRAFT GAS-FIRED BOILERS
Models N750-MFD through N3000-MFD
P-K MODU-FIRE FORCED-DRAFT GAS-FIRED WATER HEATERS
Models W750-MFD through W2000-MFD
P-K VELOX GAS-FIRED BOILERS
Models N750-VX through N2000-VX
P-K VELOX GAS-FIRED WATER HEATERS
Models W750-VX through W2000-VX
Part # 1004905935
MFD & VELOX Boilers
ASME Code, Section IV
“H” Stamp Certified by
Patterson-Kelley
C.S.A Design-Certified
Complies with ANSI
Z21.13/CSA 4.9
Gas-Fired Low Pressure
Steam and Hot Water
Boilers
C.S.A Design-Certified
Complies with ANSI
Z21.13/CSA 4.9
Gas-Fired Low Pressure
Steam and Hot Water
Boilers
MFD & VELOX Water Heaters
ASME Code, Section IV
“HLW” Stamp Certified by
Patterson-Kelley
C.S.A Design-Certified
Complies with ANSI
Z21.10.3/CSA 4.3
Gas-Fired Water
Heaters
C.S.A Design-Certified
Complies with ANSI
Z21.10.3/CSA 4.3
Gas-Fired Water Heaters
Model Number:
Serial Number:
Start-Up Date:
Harsco Industrial, Patterson-Kelley
155 Burson Street
East Stroudsburg, PA 18301
Telephone: 570.476.7261
Toll Free: 877.728.5351
Fax: 570.476.7247
www.harscopk.com
Released May 19, 2016
INSTALLATION
& O W N E R’S
MANUAL
INSTALLATION
& O W N E R’S
MANUAL
INSTALLATION
& O W N E R’S
MANUAL
INSTALLATION
& O W N E R’S
MANUAL
INSTALLATION
& O W N E R’S
MANUAL
INSTALLATION
& O W N E R’S
MANUAL
INSTALLATION
& O W N E R’S
MANUAL
INSTALLATION
& O W N E R’S
MANUAL
 HARSCO Industrial, Patterson-Kelley 2016: All Rights Reserved.
The information in this manual is the property of Harsco Industrial Patterson-Kelley. The descriptions and specifications contained in this manual were in
effect at the time this manual was approved for publication. While Harsco Industrial Patterson-Kelley will continue to support earlier model appliances to
within a reasonable time limit, we reserve the right to discontinue models and replacement parts at any time or change specifications or design without
notice and without incurring any obligation.
P-K MFD/VELOX Gas Fired Appliance
Technical Service 1.877.728.5351
Safety
General
NOTICE!
All P-K MODU-FIRE FORCED-DRAFT® & VELOXTM Gas-Fired
Boilers and Water Heaters must be:
• Installed, operated, and serviced in accordance with the
instructions contained in this manual and any other
supplemental manuals.
• Installed by qualified personnel in accordance with designs
prepared by qualified facility engineers including: structural,
mechanical, electrical, and other applicable disciplines.
• Operated and serviced in accordance with a comprehensive
safety program determined and established by the customer.
Do not attempt to operate or service until such a program
has been established.
• Operated and serviced by experienced, qualified, and
properly trained personnel in accordance with all applicable
codes, laws, and regulations.
Each safety device must be
maintained and checked per the
recommended schedule. Refer to
Section 5.2.
Safety Precautions
Provide a suitable location for the appliance, away from normal
personnel traffic, with adequate working space, adequate
clearances, proper ventilation and lighting, with a structure
sufficiently strong and rigid to support the weight of the appliance,
all piping, and accessories.
SAFETY FEATURES
It is the responsibility of the
customer to ensure external
safety provisions, such as but not
limited to: guards, safety labels,
safety controls, interlocks, lockout
devices are in place and operable.
SAFETY LABELS
The following words are used in
this manual to denote the degree
of seriousness of the individual
hazards.
Indicates an imminently
hazardous situation which,
if not avoided, will result in
death or serious injury. This
signal word is to be limited
to the most extreme
situations.
Indicates a potentially
hazardous situation which, if
not avoided, could result in
death or serious injury.
Indicates a potentially
hazardous situation which, if
not avoided, may result in
minor or moderate injury. It may
also be used to alert against
unsafe practices.
NOTICE/NOTE - NOTICE
Is the preferred signal word to
address practices not related to
personal injury. The safety alert
symbol is not used with this signal
word.
P-K MFD/VELOX Gas Fired Appliance
Technical Service 1.877.728.5351
NOTICE!
Training
The safety labels shown below are
affixed to your appliance. Although
the labels are of high quality, they
may become dislodged or
unreadable over time. Contact
Harsco Industrial, Patterson-Kelley
at 570.476.7261 or toll-free at
877.728.5351 for replacements.
Proper training is the best protection against accidents. It is
essential to read, understand, and follow the recommendations
of this manual before installing, operating, or servicing this
equipment. Failure to do so could result in fire or explosion and
serious injury, death, and/or property damage.
Operating and service personnel must be thoroughly familiar with
the basic construction of the MODU-FIRE Forced-Draft and
VELOX gas-fired boilers and water heaters, the use and
locations of the controls, the operation of the equipment,
adjustment of their various mechanisms, and all applicable safety
precautions. If any of the provisions of this manual are not fully
and completely understood, contact Harsco Industrial, PattersonKelley Technical Service at 570.476.7261 or toll free at
877.728.5351.
Hazard Warnings
Electrical Hazards
Shock Hazard! Properly lockout/tagout the
electrical service and all other energy sources
before working on or near the appliance.
Shock Hazard! Do not spray water directly on this
appliance or any electrical components.
Electrical Hazard! Do not alter wiring connections.
Crush Hazards
Lifting Hazards! Use properly rated lifting
equipment to lift and position the appliance. The
load is unbalanced. Test the balance before lifting
off the floor. Do not allow personnel beneath the
lifted load. Refer to the approximate weights in the
table below.
Gas may lose its odor. Proper gas
sensing equipment and procedures
should be used for leak checks.
Failure to detect gas leaks could
result in injury or death.
750 & 1000
1500
1700 & 2000
2500 & 3000
750 Lbs
920 Lbs
935 Lbs
1200 Lbs
Bump Hazard from Overhead Ductwork and Piping
Injury Hazard! Install components with adequate
vertical clearance.
Pressure Hazards
Pressure Hazard! Hot fluids. Install isolation valves on appliance water inlet and outlet. Make
sure isolation valves are closed before servicing the appliance.
Pressure Hazard! Hot fluids. Annually test safety relief valve(s) for proper operation. Do not
operate the appliance with faulty relief valve(s).
P-K MFD/VELOX Gas Fired Appliance
Technical Service 1.877.728.5351
Slip, Fall Hazards
Tripping Hazard! Do not install piping on floor surfaces. Maintain a clear path around the
appliance.
Slip and Fall Hazard! Use a drip pan to catch water while draining the appliance. Maintain dry
floor surfaces.
Slip and Fall Hazard! Do not locate intake or exhaust terminations above a walkway; dripping of
condensate can cause icing of the walking surface. Refer to Section 2.5.6.
Fall Hazard! Do not stand on the appliance.
Chemical Hazards
Chemical Hazards from Cleaning Products. Use
caution when cleaning the system. The use of
professional assistance is recommended. Use safe
procedures for the disposal of all cleaning solutions.
Burn, Fire and Explosion Hazards
Burn, fire, and explosion hazards! Installation must be in strict conformance to all applicable
codes and standards including NFPA 54, ANSI Z223.1 and CAN/CSA B.149. Install all required vent
lines for gas devices. Refer to Section 3.4 and Section 3.5.
Hazard from Incorrect Fuels! Possible fire, explosion, overheating, and damage. Do not use any
fuels except the design fuels for the unit.
Overfire Hazards! High pressure in gas supply could result in overfiring of this or other devices
supplied from the same source.
Fire and Explosion Hazards! Close the main gas shutoff before servicing the appliance.
Fire and Explosion Hazards! Do not store or use gasoline or other flammable vapors or liquids in
the vicinity of this or any other gas fired appliance.
Burn hazard! Possible hot surfaces. Do not touch gas vent during firing operation. Use only factory
recommended vent components.
Burn Hazard! Pipes, vents, and appliance components could be hot. Do not touch piping or stack
surfaces during operation or immediately after shutdown of the appliance.
Burn Hazard! Hot flue! Use caution when servicing or draining the appliance.
Fire and Explosion Hazards! Use caution when servicing burner. Propane (LPG) is heavier than
air and may linger in the combustion chamber, vent lines, or elsewhere.
Gas Leak Hazard! Make sure the burner is installed correctly and blower/transition is securely
fastened following any maintenance performed on them. These connections may leak gas if
assembled incorrectly.
Gas Leak Hazard! All threaded gas connections must be made using a pipe compound that is
resistant to liquefied petroleum gas. Do not use Teflon™ tape on threaded gas piping.
Gas Leak Hazard! Check entire gas train for leaks after installation. If there is a smell of gas, shut
down the appliance and obtain immediate assistance from trained service personnel and/or your
local fire department.
Overfire Hazard! Possible fire and explosion from excess gas pressure. Make sure that gas inlet
pressure does not exceed 14 inches W.C.
Overfire Hazard! Possible fire and explosion. Possible malfunction of regulators and/or gas safety
shut off/control valves. Maintain all gas train components in good condition. Do not alter wiring
connections. Annual inspection by factory-trained personnel for proper set-up and operation is
recommended.
Overfire and Underfire Hazards! Possible fire, explosion, overheating, and component failure. Do
not attempt to adjust firing rate of the appliance. The firing rate must be adjusted only by factorytrained personnel.
P-K MFD/VELOX Gas Fired Appliance
Technical Service 1.877.728.5351
Table of Contents
1
INTRODUCTION .......................................................................................... 1
1.1
1.2
1.3
2
REFERENCE TABLE – ALL MODU-FIRE FORCED DRAFT “MFD” & VELOX MODELS .................... 2
PURPOSE OF THIS DOCUMENT .................................................................................................. 3
COMMON ABBREVIATIONS ........................................................................................................ 3
SITE PREPARATION ................................................................................... 4
2.1
INITIAL INSPECTION UPON RECEIVING........................................................................................ 4
2.2
STORAGE PRIOR TO INSTALLATION ............................................................................................ 4
2.3
COMPLIANCE WITH CODES........................................................................................................ 5
2.3.1 MFD & VELOX Series: Boiler Specific Certifications ........................................................... 5
2.3.2 MFD & VELOX Series: Water Heater Specific Certifications ............................................... 5
2.3.3 Installation Codes ............................................................................................................... 6
2.4
LOCATION SETUP ..................................................................................................................... 7
2.4.1 Foundation ......................................................................................................................... 7
2.4.2 Clearances ......................................................................................................................... 8
2.5
INLET AIR AND EXHAUST VENTING CONSIDERATIONS .................................................................. 9
2.5.1 Applicable Codes and Standards ........................................................................................ 9
2.5.2 Combustion Air Inlet Planning (United States and Canada Considerations) ....................... 9
2.5.3 Category I Flue Gas Exhaust Vent Planning (VELOX Boilers & Water Heaters) ............... 10
Vent Sizing for Category I Operation (VELOX Boilers & Water Heaters Only) .......................... 10
2.5.4 Category II/IV Flue Gas Exhaust Vent Planning (MFD Boilers & Water Heaters) .............. 11
Vent Sizing for Category II / IV Operation (MFD Boilers & Water Heaters Only) ....................... 11
2.5.5 Venting Materials for Flue/Exhaust Systems ..................................................................... 12
2.5.6 Required Clearances ........................................................................................................ 13
2.6
GAS PIPING CONSIDERATIONS ................................................................................................ 15
2.7
WATER QUALITY STANDARD ................................................................................................... 15
3
INSTALLATION .......................................................................................... 16
3.1
OVERVIEW ............................................................................................................................. 16
3.2
APPLIANCE CONNECTIONS ...................................................................................................... 16
3.2.1 Appliance Connections (750 & 1000 Sizes) ...................................................................... 17
3.2.2 Appliance Connections (1500, 1700 & 2000 Sizes) .......................................................... 18
3.2.3 Appliance Connections (N2500-MFD & N3000-MFD) ....................................................... 19
3.3
ELECTRICAL CONNECTIONS .................................................................................................... 20
3.3.1 Power Requirements ........................................................................................................ 20
3.3.2 High Voltage (TB2) Terminal Block ................................................................................... 21
3.3.3 Low Voltage (TB1) Terminal Block .................................................................................... 23
3.4
COMBUSTION AIR ................................................................................................................... 25
3.4.1 Air Inlet Requirements – United States ............................................................................. 25
3.4.2 Air Inlet Requirements - Canada ....................................................................................... 26
3.4.3 MFD & VELOX Combustion Air Requirements ................................................................. 27
3.4.4 Direct Vent / Sealed Combustion Installations .................................................................. 28
3.4.5 Motorized Combustion Air Dampers ................................................................................. 30
3.5
FLUE GAS / EXHAUST VENTING .................................................................................................... 32
3.5.1 Category I Vent Installation (VELOX Boilers and Water Heaters Only) ............................. 33
3.5.2 VELOX Boilers & Water Heaters: Acceptable Category I Vent Configurations .................. 34
3.5.3 Category II or IV Vent Installation (MFD Boilers and Water Heaters Only) ........................ 36
3.5.4 MFD Boilers & Water Heaters: Acceptable Category II/IV Vent Configurations ................. 38
3.5.5 Venting for Multiple Appliances ......................................................................................... 40
3.6
REMOVING AN EXISTING BOILER OR W ATER HEATER ............................................................... 41
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
1004905935 P-K MFD & VELOX 750-3000
Installation and Owners Manual (Rev B May2016).doc
Page v
P-K MFD/VELOX Gas Fired Appliance
Technical Service 1.877.728.5351
3.7
PIPING................................................................................................................................... 42
3.7.1 Gas Piping Overview ........................................................................................................ 42
3.7.2 Natural Gas Piping ........................................................................................................... 43
3.7.3 Propane Gas Piping ......................................................................................................... 43
3.7.4 Pressure Testing the Gas Piping ...................................................................................... 43
3.7.5 Sample Piping Diagram – MFD & VELOX Series Boilers.................................................. 44
3.7.6 Sample Piping Diagram – MFD & VELOX Series Water Heaters ...................................... 45
3.7.7 Water Piping Accessories & Connections (for Installer) .................................................... 46
3.8
WATER QUALITY .................................................................................................................... 47
3.9
PRE-START CHECKLIST .......................................................................................................... 47
3.10 SAFETY CHECKS .................................................................................................................... 48
3.10.1
Ignition Safety System Test .......................................................................................... 48
3.10.2
Manual Reset High Temperature Limit Test ..................................................................... 48
3.10.3
Low Gas Pressure Switch Test ..................................................................................... 49
3.10.4
High Gas Pressure Switch Test .................................................................................... 49
3.10.5
Low Water Cut-out Test (If Applicable).......................................................................... 49
3.11 BURNER ADJUSTMENT............................................................................................................ 50
3.11.1
Inlet Gas Test Port ........................................................................................................ 50
3.11.2
Manual Control Mode for High and Low Fire Adjustment .............................................. 51
3.11.3
Adjusting High Fire Combustion.................................................................................... 52
3.11.4
Adjusting Low Fire ........................................................................................................ 52
3.11.5
Checking Flame Signal ................................................................................................. 52
3.12 INITIAL NURO CONTROL SETUP & ADJUSTMENT ...................................................................... 53
3.12.1
Startup .......................................................................................................................... 53
3.12.2
Home Screen................................................................................................................ 54
3.12.3
Information Screen ....................................................................................................... 54
3.12.4
Setup Wizard ................................................................................................................ 55
4
OPERATIONS ............................................................................................ 56
4.1
NURO TOUCHSCREEN CONTROL SYSTEM............................................................................... 56
4.1.1 Power On/Off Switch ........................................................................................................ 56
4.1.2 NURO Touch Screen Interface and Control Panel ............................................................ 57
4.1.3 Factory Tests .................................................................................................................... 57
4.2
NORMAL LIGHTING AND SHUT-DOWN PROCEDURES ................................................................. 58
4.2.1 Normal Lighting Procedures ............................................................................................. 58
4.2.2 Normal Shut Down Procedures......................................................................................... 58
4.3
EMERGENCY SHUT-OFF ......................................................................................................... 58
5
MAINTENANCE ......................................................................................... 59
5.1
PREVENTATIVE MAINTENANCE ................................................................................................ 59
5.1.1 Daily Preventative Maintenance ....................................................................................... 59
5.1.2 Weekly Preventative Maintenance .................................................................................... 59
5.1.3 Monthly Preventative Maintenance ................................................................................... 60
5.2
MAINTENANCE AND INSPECTION SCHEDULE ............................................................................. 61
5.2.1 Semi-Annually .................................................................................................................. 61
5.2.2 Annually ........................................................................................................................... 61
5.3
CLEANING THE BURNER & COMBUSTION CHAMBER .................................................................. 62
5.4
AFTER REPAIRS OR MAINTENANCE.......................................................................................... 67
5.5
SEQUENCE OF OPERATIONS ................................................................................................... 67
5.6
TROUBLESHOOTING ............................................................................................................... 69
5.6.1 Loss of Power ................................................................................................................... 69
5.6.2 Loss of Water Flow ........................................................................................................... 69
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
1004905935 P-K MFD & VELOX 750-3000
Installation and Owners Manual (Rev B May2016).doc
Page vi
P-K MFD/VELOX Gas Fired Appliance
Technical Service 1.877.728.5351
5.6.3
5.6.4
5.6.5
5.6.6
5.6.7
5.6.8
5.6.9
6
Low Gas Pressure ............................................................................................................ 69
High Gas Pressure ........................................................................................................... 69
High Water Temperature ................................................................................................... 69
Low Air ............................................................................................................................. 70
Flame Failure ................................................................................................................... 70
Flame Error ...................................................................................................................... 70
Flue Problem .................................................................................................................... 70
PARTS/TECHNICAL SUPPORT ................................................................ 71
6.1
TERMINAL BLOCK ASSIGNMENTS AND W IRING DIAGRAMS ......................................................... 72
6.1.1 Terminal Block Assignments — High Voltage (TB2) Terminal Block .................................. 73
6.1.2 Terminal Block Assignments — Low Voltage (TB1) Terminal Block .................................. 74
6.1.3 MFD/VELOX NURO Wiring Diagram ................................................................................ 75
6.2
PARTS IDENTIFICATION .......................................................................................................... 76
6.2.1 Main Assembly ................................................................................................................. 76
6.2.2 NURO Control Panel ........................................................................................................ 77
6.2.3 Heat Exchanger Assembly (Sizes 750 through 2000) ....................................................... 78
6.2.4 Heat Exchanger Assembly (Sizes 2500 & 3000)............................................................... 79
6.2.5 Gas Train, Burner & Blower Assembly (Sizes 750 through 2000) ..................................... 80
6.2.6 Gas Train, Burner & Blower Assembly (Sizes 2500 & 3000) ............................................. 81
7
MODU-FIRE FORCED DRAFT & VELOX LIMITED WARRANTY............. 82
8
FIRE-TEST REPORT ................................................................................. 84
APPENDIX A – MAINTENANCE LOG ............................................................. 85
APPENDIX B –ALTITUDE DERATE SCHEDULE ........................................... 86
APPENDIX C –WATER QUALITY STANDARD FOR HYDRONIC BOILERS IN
MULTI-METAL SYSTEMS ............................................................................... 87
APPENDIX D – BEST PRACTICES FOR NEW & RETROFIT SYSTEMS ...... 88
APPENDIX E – INSTALLATION AND QUICK REFERENCE .......................... 91
FUEL/GAS SUPPLY ............................................................................................................................ 91
ELECTRICAL/POWER SUPPLY ............................................................................................................. 91
EXHAUST VENTING ............................................................................................................................ 91
HYDRONICS/W ATER FLOW (MFD & VELOX 750 - 1000 SIZES) ............................................................ 92
APPLIANCE CONNECTIONS (MFD & VELOX 750 - 1000 SIZES) ............................................................ 93
HYDRONICS/W ATER FLOW (MFD & VELOX 1500 - 2000 SIZES) .......................................................... 94
APPLIANCE CONNECTIONS (MFD & VELOX 1500 - 2000 SIZES) .......................................................... 95
HYDRONICS/W ATER FLOW (N2500-MFD & N3000-MFD).................................................................... 96
APPLIANCE CONNECTIONS (N2500-MFD & N3000-MFD) .................................................................... 97
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
1004905935 P-K MFD & VELOX 750-3000
Installation and Owners Manual (Rev B May2016).doc
Page vii
P-K MFD/VELOX Gas Fired Appliance
Technical Service 1.877.728.5351
1 Introduction
If the information in this manual
is not followed, fire or
explosion may result causing
property damage, personal
injury, or loss of life.
Do not store or use gasoline or other
flammable vapors or liquids in the
vicinity of this or any other appliance.
Installation and service must be
performed by a qualified installer,
service agency, or the gas supplier.
WHAT TO DO IF YOU SMELL GAS:


Do not try to light any appliance.
Do not touch any electrical
switch; do not use any phone in
your building.
 Immediately call your gas
supplier from a neighbor’s
phone. Follow the gas supplier’s
instructions.
If you cannot reach your gas
supplier, call the fire department.
It is essential to read,
understand, and follow the
recommendations of this
manual before installing,
operating or servicing this
equipment. Failure to do so
could result in personal injury
or death.
Installation and service must be
performed by a qualified and
knowledgeable individual who
has been certified on the P-K
appliance. The features which
permit this appliance to achieve
high-efficiency performance
can be misused which could
result in personal injury or
death.
Revised: May 19, 2016
Release May 17, 2016
This manual describes the installation and operation of P-K
MODU-FIRE Forced Draft “MFD” and VELOX series boilers and
water heaters featuring NURO controls:
MFD Boilers
Category II or IV Venting
See Section 1.1 for modulation
ANSI Z21.13 / CSA 4.9
ASME “H” Stamp
160 PSI Maximum Pressure
250°F Maximum Temperature
VELOX Boilers
Category I Venting
See Section 1.1 for modulation
ANSI Z21.13 / CSA 4.9
ASME “H” Stamp
160 PSI Maximum Pressure
250°F Maximum Temperature
MFD Water Heaters
Category II or IV Venting
See Section 1.1 for modulation
ANSI Z21.10.3 / CSA 4.3
ASME “HLW” Stamp
160 PSI Maximum Pressure
210°F Maximum Temperature
VELOX Water Heaters
Category I Venting
See Section 1.1 for modulation
ANSI Z21.10.3 / CSA 4.3
ASME “HLW” Stamp
160 PSI Maximum Pressure
210°F Maximum Temperature
Individual differences between each model will be called out and
defined in separate sections and the titles of these sections will
include the applicable model number. If model numbers are not
listed in the section title, that section is common to all models.
If you have any questions on the information contained within, or
do not fully and completely understand the content, please
contact Harsco Industrial, Patterson-Kelley Technical Service at
570.476.7261 or toll free at 877.728.5351.
The MODU-FIRE Forced Draft and VELOX gas-fired appliance is
fully modulating using a variable speed combustion blower,
sophisticated microprocessor controls, modulating gas safety shut
off / control valves and a time tested copper finned-tube heat
exchanger. The high-quality materials and state of the art design
should provide years of trouble-free service if the instructions in
this manual are followed carefully.
This appliance is only a part of the complete hydronic or domestic
water system. This appliance may be fully operational and yet
because of poor circulation, improper control, or other site related
characteristics, not deliver heat to the desired location. Additional
equipment such as temperature sensors, pumps, flow switches,
balancing valves, and check valves will be required for
satisfactory operation of any system. Harsco Industrial, PattersonKelley cannot be responsible for the design or operation of such
systems and a qualified engineer or contractor must be consulted.
While details may differ slightly, basic operation is the same for all
models. Most models may be built to operate with natural gas or
liquefied petroleum gas (propane). Check the rating plate for
correct fuel type and gas pressures.
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
1004905935 P-K MFD & VELOX 750-3000
Installation and Owners Manual (Rev B May2016).doc
Page 1
P-K MFD/VELOX Gas Fired Appliance
Technical Service 1.877.728.5351
1.1 Reference Table – All MODU-FIRE Forced Draft “MFD” & VELOX
Models
Model
Number
N750-MFD
N1000-MFD
N1500-MFD
N2000-MFD
N2500-MFD*
N3000-MFD*
Vent
Category
Max Input
Rating
(Btu/hr)
Min Input
Rating
(Btu/hr)
Effective
Turndown
Ratio
Max
Output
Rating
(Btu/hr)
Efficiency
MFD Boilers: ASME “H” Stamp & ANSI Z21.13 / CSA 4.9
II or IV
750,000
150,000
5:1
637,500
II or IV
1,000,000
166,000
6:1
850,000
II or IV
1,500,000
250,000
6:1
1,275,000
II or IV
2,000,000
335,000
6:1
1,700,000
II or IV
2,500,000
500,000
5:1
2,200,000
II or IV
3,000,000
500,000
6:1
2,640,000
N750-VX
N1000-VX
N1500-VX
N1700-VX
N2000-VX
Recovery
Rating
(GPH)
40°F to
140°F
85%
85%
85%
85%
88%
88%
N/A
N/A
N/A
N/A
N/A
N/A
VELOX Boilers: ASME “H” Stamp & ANSI Z21.13 / CSA 4.9
I
750,000
604,000
1.2:1
637,500
85%
I
1,000,000
610,000
1.6:1
850,000
85%
I
1,500,000 1,005,000
1.5:1
1,275,000
85%
I
1,700,000 1,050,000
1.6:1
1,445,000
85%
I
2,000,000 1,100,000
1.8:1
1,700,000
85%
N/A
N/A
N/A
N/A
N/A
W750-MFD
W1000-MFD
W1500-MFD
W2000-MFD
MFD Water Heaters: ASME “HLW” Stamp & ANSI Z21.13 / CSA 4.9
II or IV
750,000
150,000
5:1
637,500
85%
II or IV
1,000,000
166,000
6:1
850,000
85%
II or IV
1,500,000
250,000
6:1
1,275,000
85%
II or IV
2,000,000
335,000
6:1
1,700,000
85%
772.5
1030
1545
2060
W750-VX
W1000-VX
W1500-VX
W1700-VX
W2000-VX
VELOX Water Heaters: ASME “HLW” Stamp & ANSI Z21.13 / CSA 4.9
I
750,000
604,000
1.2:1
637,500
85%
I
1,000,000
610,000
1.6:1
850,000
85%
I
1,500,000 1,005,000
1.5:1
1,275,000
85%
I
1,700,000 1,050,000
1.6:1
1,445,000
85%
I
2,000,000 1,100,000
1.8:1
1,700,000
85%
772.5
1030
1545
1750
2060
**NOTE: Models N2500-MFD & N3000-MFD are only approved for use with Natural Gas.
All other models can be ordered for Natural Gas or Propane Gas.
Revised: May 19, 2016
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1.2 Purpose of this Document
The purpose of this Installation and Owner’s Manual is to provide comprehensive documentation
support for the P-K MODU-FIRE Forced Draft & VELOX series of gas fired boilers and water heaters
featuring NURO controls. This manual discusses requirements for all installations as well as
recommended best practices for installation, operation and maintenance.
The primary concern of all Harsco Industrial, Patterson-Kelley equipment installation procedures is
safety. Safety instructions and considerations are presented and repeated throughout the document as
required. If you have any questions on the information contained within, or do not fully and completely
understand the content, please contact Harsco Industrial, Patterson-Kelley Technical Service at
570.476.7261 or toll free at 877.728.5351.
1.3 Common Abbreviations
Abbreviation
Description
AMP
Ampere or Amperage
ANSI
American National Standards Institute
ASME
American Society of Mechanical Engineers
AWG
American Wire Gauge
BTU
British Thermal Unit
CH
Comfort Heat
CO2
Carbon Dioxide
CSA
Canadian Standards Association
CSD-1
Controls and Safety Devices
CPVC
Chlorinated Polyvinyl Chloride
DHW
Domestic Hot Water
HWR
Heating Water Return / Hot Water Return (From Building)
HWS
Heating Water Supply / Hot Water Supply (To Building)
ID
Inside Diameter
MBH
Thousands of BTU / Hour
MFD
MODU-FIRE Forced-Draft Series Boiler or Water Heater
MODBUS
A serial communication protocol (not an abbreviation)
NFPA
National Fire and Protection Agency
NTC
Negative Temperature Coefficient
O2
Oxygen
OD
Outside Diameter
OEM
Original Equipment Manufacturer
SCFM
Standard Cubic Feet per Minute
SMACNA
Sheet Metal and Thermoplastic Duct Construction Manual Air Conditioning
Contractors National Association
TB<#>
Terminal Block (1, 2, 3 etc.)
VAC
Volts Alternating Current
VDC
Volts Direct Current
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2
Installation and service must be
performed by a qualified
installer, service agency, or gas
supplier. Failure to install the
equipment in accordance with
this manual could result in an
unsafe operating condition.
The appliance is heavy and
requires additional technicians
to support and move the unit(s)
during installation. Use extreme
caution to avoid dropping the
appliance or cause any bodily
injury while lifting or handling.
When positioning this
appliance, maintain positive
control of it at all times. Do not
attempt to move the boiler on
surfaces that are not level.
Failure to heed this warning
could result in personal injury
or death.
Site Preparation
2.1 Initial Inspection Upon Receiving
Upon receiving the appliance, inspect it for signs of shipping
damage. Some damage may be hidden. Unpack the appliance,
open the front and side doors and inspect the appliance. Verify
that the total number of pieces shown on the packing slip agrees
with those actually received.
NOTICE! Note any damage, suspected potential damage, or
shortage of materials on the freight bill and immediately notify
the carrier. File all claims for shortage or damage with the
carrier. Claims for hidden damages must be filed with your
carrier within 7 days. The carton is equipped with a “Tip (N)
Tell”. If the “Tip (N) Tell” arrow point is blue, that indicates the
package has been on its side or tipped over in transit.
2.2 Storage Prior to Installation
If the appliance is not installed immediately, it must be stored in a
location adequately protected from the weather, preferably
indoors. If this is not possible, then it should remain in the
shipping container and be covered by a tarpaulin or other
waterproof covering.
NOTICE! Controls and other equipment that are damaged or
fail due to weather exposure are not covered by warranty.
NOTICE!
The appliance may be installed on a
combustible floor; however, the
appliance must never be installed on
carpeting.
Bumping hazard from overhead
ducts! Install all components
with adequate vertical
clearances. Insufficient
clearance can restrict the
service access, increasing the
possibility of injury.
Revised: May 19, 2016
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2.3 Compliance with Codes
MFD & VELOX Series
MFD & VELOX Series
Boilers
Water Heaters
ASME Section IV – “H”
ASME Section IV – “HLW”
(Latest Edition)
(Latest Edition)
ANSI Z21.13 / CSA 4.9
ANSI Z21.10.3 / CSA 4.3
(Latest Edition)
(Latest Edition)
160 PSIG
160 PSIG
Maximum Allowable Design
Temperature
250°F
210°F
Maximum Setpoint
220°F
190°F
Hi-limit Setpoint
240°F
197°F
Suitable for Potable Water?
NO
YES
Code of Construction
CSA/ANSI Specification
Maximum Allowable
Working Pressure
2.3.1 MFD & VELOX Series: Boiler Specific Certifications
The “N Series” MODU-FIRE Forced-Draft and VELOX boilers with standard components comply with
American National Standard/CSA Standard ANSI Z21.13/CSA 4.9, latest edition. The heat exchanger
is not suitable for use with potable water and is constructed and “H” stamped in accordance with ASME
Boiler and Pressure Vessel Code, Section IV for 160 psig maximum pressure and 250°F maximum
temperature. Other codes or approvals which apply will be labeled on the boiler.
2.3.2 MFD & VELOX Series: Water Heater Specific Certifications
The “W Series” MODU-FIRE Forced-Draft and VELOX water heaters with standard components
comply with American National Standard/CSA Standard ANSI Z21.10.3/CSA 4.3, latest edition. The
heat exchanger is suitable for use with potable water and is constructed and “HLW” stamped in
accordance with ASME Boiler and Pressure Vessel Code, Section IV for 160 psig maximum pressure
and 210°F maximum temperature. Other codes or approvals which apply will be labeled on the water
heater.
NOTE: The appliance should be located in an area where leakage of the tank or connections
will not result in damage to the area adjacent to the appliance or to lower floors of the structure.
When such locations cannot be avoided, it is recommended that a suitable drain pan,
adequately drained, be installed under the appliance. The pan must not restrict combustion air
flow.
NOTE: If a water heater is installed in a closed water supply system, such as one having a
backflow preventer in the cold water supply line, means shall be provided to control thermal
expansion. Contact the water supplier or local plumbing inspector on how to control this
situation.
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NOTE: For tube type circulating water heaters installed only with a pressure relief valve, the
separate storage vessel must have a temperature and pressure relief valve installed. This relief
valve shall comply with the Standard for Relief Valves for Hot Water Supply Systems, ANSI
Z21.22 • CSA 4.4. (Also see Clauses 4.21.4 and 4.21.5.)
2.3.3 Installation Codes
Installation of the boiler or water heater must conform to all the requirements of all national, state, and
local codes established by the authorities having jurisdiction or, in the absence of such requirements, to
the National Fuel Gas Code, ANSI Z223.1/NFPA 54 latest edition in the U.S. In Canada, the equipment
shall be installed in accordance with the current Installation Code for Gas Burning Appliances and
Equipment, CAN/CSA-B.149, latest edition, and applicable Provincial Regulations for the class, which
should be carefully followed in all cases. Authorities having jurisdiction should be consulted before
making any installation.
Where required by local codes, the installation must conform to American Society of Mechanical
Engineers Safety Code for Controls and Safety Devices for Automatically Fired Boilers (ASME CSD-1).
In the Commonwealth of Massachusetts (a) this unit must be installed by a licensed pipe fitter/plumber,
(b) field installed gas cocks must be “T” handle type, (c) piping of condensate shall conform to the State
Plumbing Code, and (d) refer to the Massachusetts Supplement for further details.
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2.4 Location Setup
2.4.1 Foundation
Provide a firm, level foundation, preferably made of concrete. The MODU-FIRE Forced Draft and
VELOX boilers and water heaters must be level and upright to function properly. There are 3/4” holes
at the four corners of the structural steel c-channel base for anchoring and leveling as shown below.
Once the appliance is installed on the foundation and furnished with anchor/lag bolts, use a bubble
level and adjust the four anchor nuts until the appliance is secure and level.
3/4” Hole for
Anchor/Lag Bolts
(Rear Right Corner)
3/4” Hole for
Anchor/Lag Bolts
(Rear Left Corner)
3/4” Hole for
Anchor/Lag Bolts
(Front Left Corner)
3/4” Hole for
Anchor/Lag Bolts
(Front Right Corner)
NOTICE! The appliance may be installed on a combustible floor; however, the appliance must
NEVER be installed on carpeting.
NOTICE! This appliance is certified for INDOOR use only!
Revised: May 19, 2016
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2.4.2 Clearances
If the boiler or water heater is to be installed near combustible surfaces, there must be twenty-four (24”)
inches minimum clearance. Failure to provide adequate service clearances, even with non-combustible
surfaces, may present problems during routine maintenance of the appliance. The appliance must be
installed in a space large in comparison to the appliance as described in the National Fuel Gas Code,
NFPA 54/ANSI Z223.1, Latest Edition.
Dimensions (inches)
Type of Surface
A
B
C†
D**
E**
CSA Minimum Clearances to Combustibles
24
24
24
24
24
Clearance to Non-Combustible Surfaces
0
0
0
0
0
Recommended Service Clearances
36
24*
24
24**
24**
† “C" dimension includes clearance to remove the burner. Do not put pipes, ducts, etc. in area above the
appliance.
*CSA minimum. Actual clearance depends upon venting requirements.
** Left & Right-Side service access (“D” & “E” Dimension”) are needed to view the appliance’s runout &
safety warning labels, and access the electrical junction box.
Note: Failure to provide recommended service clearances may make it difficult to perform
service on the appliance(s).
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2.5 Inlet Air and Exhaust Venting Considerations
Design and installation of
venting systems should be
done only by qualified and
knowledgeable venting systems
personnel and in accordance
with the vent system
manufacturer’s installation
instructions. Installing an
appliance or vent system using
improper installation methods
or materials can result in
serious injury or death due to
fire or asphyxiation.
Before connecting an appliance
to a venting system, it must be
determined whether the
appliance is to be installed in a
conventional or direct vent
configuration. In the US,
provisions for combustion air
must be in accordance with
NFPA 54/ANSI Z223.1, National
Fuel Gas Code, latest edition,
or applicable provisions of
local building codes. In
Canada, combustion and
ventilation air openings shall
comply with CAN/CSA B-149.1
Natural Gas and Propane
Installation Code.
For correct installation of a vent
system, read all of these
instructions and refer to the
vent manufacturer’s
instructions.
2.5.1 Applicable Codes and Standards
United States Installation Codes:
NBIC – Part I
NFPA 54/ANSI Z223.1
NFPA/ANSI 211
National Board Inspection Code - Installation
National Fuel Gas Code
Chimneys, Fireplaces, Vents and Solid Fuel Burning
Appliances
Canada Installation Codes:
CAN/CSA B149.1
Installation Codes for Gas Burning Equipment
Flue Gas Exhaust Vent Standards:
UL 441 / ULC S605
ULC S636
UL 1738
Standard for Gas Vents
Standard for Type BH Gas Venting Systems
Venting Systems for Gas-Burning Appliances,
Categories II, III and IV
These codes and standards contain information for the venting of gas
fired appliances, including, but not limited to vent sizing, location,
clearance to combustibles, and safe installation practices. The installation
must comply with both the above Federal Codes and with state,
provincial, and local codes.
2.5.2 Combustion Air Inlet Planning (United States and
Canada Considerations)


Air inlet considerations for the United States are established by
NFPA 54/ANSI Z223.1 & NFPA/ANSI 211.
Air inlet requirements for Canada are established by CAN/CSA
B149.1.
Refer to Section 3.4 for more details on combustion air inlet requirements
in the United States and Canada.
Failure to use a proper vent
system (types and materials),
as described in this manual will
void the warranty and may
result in rapid deterioration of
the venting system, creating a
health or life safety hazard.
Faulty vent installation can
allow toxic fumes to be
released into living areas. This
may cause property damage,
injury, or death.
Revised: May 19, 2016
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2.5.3 Category I Flue Gas Exhaust Vent Planning (VELOX Boilers & Water Heaters)
Several codes and standards, e.g. NFPA 54/ANSI Z223.1 categorize appliances in accordance with the
flue gas temperature and pressure produced by the appliance, which are defined as follows:
VELOX Boilers & Water Heaters

Category I: An appliance that operates with a non-positive vent static pressure and with a vent
gas temperature that avoids excessive condensate production in the vent.

Direct Vent: An appliance that is constructed and installed so that all air for combustion is
derived directly from outdoors and all flue gases are discharged to the outdoors.
VELOX series boilers are Category I appliances, as defined in ANSI Z21.13/CSA 4.9, latest edition and
are suitable for use with Type “B” vents. VELOX series water heaters are also Category I appliances,
as defined in ANSI Z21.10.3/CSA 4.3, latest edition and are suitable for use with Type “B” vents. The
VELOX series boilers and water heaters are designed to operate under a slight negative exhaust
pressure. It is critical to ensure the flue venting material is suitable for use with the appliance.
NOTE: For Category I installations, ensure the flue venting system is designed to maintain a
slightly negative exhaust pressure between -0.01” W.C. and -0.05” W.C.
The vent material to be used for US and Canada is listed in the Table of Acceptable Materials for
Venting Systems located in Section 2.5.5.
Vent installations shall be in accordance with NFPA 54/ANSI Z223.1, the National Fuel Gas Code, or
CAN/CSA-B149.1, the Natural Gas and Propane Installation Code, or applicable provisions of the local
building codes.
Vent Sizing for Category I Operation (VELOX Boilers & Water Heaters Only)
The vent must be sized in accordance with the ASHRAE Systems and Equipment handbook (Chapter
30) or according to the vent manufacturer’s recommendations. When using manufactured venting
systems, consult your vent supplier for correct sizing and structural support requirements.
VELOX Appliance Size
750/1000/1500/1700/2000
Revised: May 19, 2016
Release May 17, 2016
Draft
Stack Temperature
CO2
Natural Gas
CO2
Propane Gas
-0.02” W.C. to -0.05”
W.C.
325 °F (gross)
8.0%
9.2%
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2.5.4 Category II/IV Flue Gas Exhaust Vent Planning (MFD Boilers & Water Heaters)
Several codes and standards, e.g. NFPA 54/ANSI Z223.1 categorize appliances in accordance with the
flue gas temperature and pressure produced by the appliance, which are defined as follows:
MODU-FIRE Forced Draft Boilers & Water Heaters

Category II: An appliance that operates with a non-positive vent static pressure and with a vent
gas temperature that may cause excessive condensate production in the vent.

Category IV: An appliance that operates with a positive vent static pressure and with a vent gas
temperature that may cause excessive condensate production in the vent.

Direct Vent: An appliance that is constructed and installed so that all air for combustion is
derived directly from outdoors and all flue gases are discharged to the outdoors.
MODU-FIRE Forced-Draft series boilers are dual-certified as Category II or IV appliances, as defined
in ANSI Z21.13/CSA 4.9, latest edition. MODU-FIRE Forced-Draft series water heaters are also dualcertified as Category II or IV appliances, as defined in ANSI Z21.10.3/CSA 4.3, latest edition. The
MFD series boilers and water heaters are capable of operating with slightly negative to slightly positive
exhaust pressure. It is critical to ensure the flue vent material is certified for Category II or IV
operation.
NOTE: For Category II installations, ensure the flue venting system is designed to maintain a
slightly negative exhaust pressure between -0.01” W.C. and -0.05” W.C.
NOTE: For Category IV installations, ensure the flue venting system is designed to maintain a
slightly positive exhaust pressure which MUST BE in the following ranges:
 +0.01” W.C. and +1.5” W.C. (MFD Sizes 750 through 2000)
 +0.01” W.C. and +1.0” W.C. (MFD Sizes 2500 & 3000).
The vent material to be used for US and Canada is listed in the Table of Acceptable Materials for
Venting Systems located in Section 2.5.5.
Vent installations shall be in accordance with NFPA 54/ANSI Z223.1, the National Fuel Gas Code, or
CAN/CSA-B149.1, the Natural Gas and Propane Installation Code, or applicable provisions of the local
building codes.
Vent Sizing for Category II / IV Operation (MFD Boilers & Water Heaters Only)
The vent must be sized in accordance with the ASHRAE Systems and Equipment handbook (Chapter
30) or according to the vent manufacturer’s recommendations. When using manufactured venting
systems, consult your vent supplier for correct sizing and structural support requirements.
Exhaust Pressure
Stack Temperature
CO2
Natural Gas
CO2
Propane Gas
750/1000/1500/2000
1.5” W.C.
325 °F (gross)
8.7%
10.0%
2500/3000
1.0” W.C.
325 °F (gross)
8.4%
N/A
MFD Appliance Size
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2.5.5 Venting Materials for Flue/Exhaust Systems
VELOX series boilers and water heaters are certified as Category I
appliances, which vents with a high gas temperature that is unlikely
to cause condensation in the vent. Therefore, any venting system
used with a VELOX series boiler or water heater MUST comply with
the requirements for Category I venting systems as specified in the
latest edition of NFPA 54/ANSI Z223.1 in the US or the latest edition
of CAN/CSA B-149.1 in Canada.
The venting materials listed are
intended for the venting of gas
burning appliances only. Do
not use these venting materials
for venting liquid or solid fuel
(such as oil, kerosene, wood,
or coal) appliances.
Maintain clearances to
MODU-FIRE Forced-Draft series boilers and water heaters are dualcombustibles as listed in the
certified as Category II or IV appliances, which vent with a gas
vent manufacturer’s
temperature that is likely to cause condensation in the vent.
installation
instructions or as
Therefore, any venting system used with a MFD series boiler or water
set forth in the codes and
heater MUST comply with the requirements for Category II or IV
standards listed in this section.
venting systems as specified in the latest edition of NFPA 54/ANSI
Z223.1 in the US or the latest edition of CAN/CSA B-149.1 in Canada. Do not use these vent pipes for
incinerators of any sort!
The use of plastic venting materials including
CPVC, PVC, PolyPropylene, etc. is
PROHIBITED! Failure to comply with this
warning could result in injury or death due to
failed flue material.
This appliance is not certified
for use with PVC venting. Use
of PVC venting may result in
vent failure and possible
serious injury or death.
The venting materials listed below are intended
for the venting of gas burning appliances only.
Do not use these venting materials for venting
liquid or solid fuel (such as oil, kerosene, wood,
or coal) appliances.
Maintain clearances to combustibles as listed in
the vent manufacturer’s installation instructions
or as set forth in the codes and standards listed
in this section. Do not use these vent pipes for
incinerators of any sort.
As per ANSI Z21.13b-2012 * CSA 4.9b-2012:
 The use of cellular core PVC, CPVC, and Radel as venting materials is prohibited.
 The use of plastic vent pipe is prohibited.
Table of Acceptable Venting Materials for VELOX & MFD Appliances
Product Series
Category
Country Type B
AL29-4C 316L SS PVC
CPVC
PP
VELOX Boilers
I
US
Yes
Note 1
Note 1
No
No
VELOX Water Heaters I
US
Yes
Note 1
Note 1
No
No
VELOX Boilers
I
Canada
Yes
Note 1
Note 1
No
No
VELOX Water Heaters I
Canada
Yes
Note 1
Note 1
No
No
No
No
No
No
MFD Boilers
II, IV
US
No
Yes
Yes
No
No
MFD Water Heaters
II, IV
US
No
Yes
Yes
No
No
MFD Boilers
II, IV
Canada
No
Yes
Yes
No
No
MFD Water Heaters
II, IV
Canada
No
Yes
Yes
No
No
No
No
No
No
Note 1: Ensure this flue material is suitable for Category I applications.
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2.5.6 Required Clearances
Conventional Vent Systems Clearances
The following termination clearance requirements are for conventional non direct-vent installations:

The vent system shall terminate at least 3 ft. above a forced air inlet located within 10 ft.
horizontally.

The vent system shall terminate at least 4 ft. below, 4 ft. horizontally from, or 1 ft. above any
door, operable window, or gravity inlet into any building. The bottom of the vent terminal shall be
at least 12 in. above grade or highest expected snow line (if applicable).

Through-the-wall terminations shall not terminate over public walkways or over an area where
condensate or vapor could create a nuisance or hazard or could be detrimental to the operation
of regulators, relief valves, or other equipment.
Direct Vent (Sealed Combustion) Systems Clearances
 The vent terminal shall be located at least 12 in. from any air opening into a building. The
bottom of the vent terminal shall be at least 12 in. above grade. Both the vent and air intake
terminals must be at least 12 in. above the highest expected snow line.

Through-the-wall terminations shall not terminate over public walkways or over an area where
condensate or vapor could create a nuisance or hazard or could be detrimental to the operation
of regulators, relief valves, or other equipment.

When multiple direct vent appliances are adjacent, the exhaust must terminate at least 10 ft.
horizontally or 3 ft. vertically from the air intake of another appliance.
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The appliance vent should
not be connected into any
portion of another
mechanical draft system
without consulting the vent
manufacturer. Improper
interconnection of venting
systems may result in
leakage of flue gases into
occupied spaces.
Mark Description
US Installations
Canadian Installations
A
Clearance to each side of center line
extended above meter/regulator
3 ft (91 cm) within a height of 15 ft (4.6
m) above the meter/regulator assembly
B
Clearance to service regulator vent outlet
3 ft (91 cm)
C
Clearance above grade, porch, deck,
veranda, or balcony
12 in
4 ft (1.2 m) below or to side
of opening
1 ft (300 mm) above
opening
6 in (15 cm) for appliances ≤ 10,000
Btuh (3 kW)
12 in (30 cm) for appliances > 10,000
Btuh (3 kW) and ≤ 100,000 Btuh (30
kW)
36 in (91 cm) for appliances > 100,000
Btuh (30 kW)
E
Clearance to non-mechanical air supply inlet
to building or the combustion air inlet to any
other appliance
4 ft (1.2 m) below or to side
of opening
1 ft (300 mm) above
opening
6 in (15 cm) for appliances ≤ 10,000
Btuh (3 kW)
12 in (30 cm) for appliances > 10,000
Btuh (3 kW) and ≤ 100,000 Btuh (30
kW)
36 in (91 cm) for appliances > 100,000
Btuh (30 kW)
F
Clearance to a mechanical air supply inlet
3 ft (91 cm) above if within
10 ft (3 m) horizontally
6 feet (1.83 m)
D
Clearance to window or door that may be
opened
For clearances not specified maintain clearance in accordance with local installation codes and the requirements of the gas supplier
Interior Component Clearances
All vent system components shall be installed so as to maintain the following required minimum
clearances:
Material
Combustible
Non-Combustibles
Unlisted single wall metal pipe
Do NOT Use
Do NOT Use
Single wall CPVC, PVC or PP pipe
Do NOT Use
Do NOT Use
UL 441 listed Category I vent
Per manufacturer’s listing
Per manufacturer’s listing
UL 1738 listed Category II or IV vent Per manufacturer’s listing
Per manufacturer’s listing
Revised: May 19, 2016
Release May 17, 2016
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All Rights Reserved.
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Flue Connection
The connection from the appliance to the vent should be as direct as possible and the upward slope of
any horizontal breaching should be at least 1/4 inch per linear foot. Examples of the complete exhaust
system with drain is Section 3.5. The appliance connector should incorporate provisions to drain
condensate formed in the vent system. The connector should include an appropriate drain section (not
provided).
2.6 Gas Piping Considerations
Before making the gas hook-up, make sure the appliance is being supplied with the type of fuel shown
on the nameplate.
Supplying a fuel other than that shown on the appliance’s nameplate
can lead to overfiring of the appliance. This can cause damage to
the equipment which could result in serious injury and/or death.
The appliance shall be installed such that the gas ignition system components are protected from water
(dripping, spraying, rain, etc.) during appliance operation and service (circulator replacement, control
adjustment, etc.).
2.7 Water Quality Standard
The appliance’s heat exchanger contains copper finned-tubing. The heat exchanger requires proper
water conditions to remain efficient and function properly. For information, please refer to Harsco
Industrial, Patterson-Kelley Multi-Metal Systems Water Quality Standards as it appears in Appendix C
as this applies to the warranty of your heat exchanger.
NOTE: Failure to maintain the water quality according to the requirements of the multi-metal
systems water quality standards can void the heat exchanger warranty.
Revised: May 19, 2016
Release May 17, 2016
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All Rights Reserved.
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3 Installation
3.1 Overview
For the preliminary site preparation, follow the guidelines discussed in Section 2. Section 3 details the
installation requirements for electrical connections, combustion air, flue vent piping, hydronic or
domestic water piping, etc.
3.2 Appliance Connections
The table below summarizes the appliance connections to the MFD & VELOX series boilers:
Boiler Size
750, & 1000
1500
1700 & 2000
Power Requirement
2500* & 3000*
12” x 12”
10”
10”
10”
208-240/1/60
Air Intake
Connection
Nominal Exhaust
Vent Connection
2500 & 3000
8”
6”
8”
8”
Recommended Flue
Size
Category I: See Section 3.5.1
Category II/IV: See Section 3.5.3
Fireside Drain Pipe
3/4” NPT-M
(Steel)
Heat Exchanger
Drain
Gas Shutoff Valve
3/4”
1-1/4” NPT-F
3/4” NPT-F
1-1/2” NPT-F
2” NPT-F
2-1/2” NPT-M
(Steel)
2-1/2” NPT-F
(Cast Iron)
HWR Connection
HWS Connection
3” 150# Flange
(Steel)
3” 150# Flange
(Cast Iron)
*With optional air intake adapter (part # 23-0000-0480) installed for a 10” circular connection.
The table below summarizes the appliance connections to the MFD & VELOX series water heaters:
Water Heater Size
Power Requirement
Air Intake Connection
Nominal Exhaust
Vent Connection
Recommended Flue
Size
Fireside Drain Pipe
Heat Exchanger Drain
Valve
Gas Shutoff Valve
HWR Connection
HWS Connection
Revised: May 19, 2016
Release May 17, 2016
750 & 1000
1500
1700 & 2000
208-240/1/60
8”
6”
8”
Category I: see table in Section 3.5.1
Category II/IV: see table in Section 3.5.3
3/4” NPT-M
(Steel)
3/4” NPT-F
1-1/4” NPT-F
2-1/2” NPT-M
(Brass)
2-1/2” NPT-F
(Nickel Plated)
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1-1/2” NPT-F
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3.2.1 Appliance Connections (750 & 1000 Sizes)
All connections must be in compliance with national, state, and local code requirements.
NOTICE!
This is a non-condensing gasfired appliance and the
incoming (return) water
temperature MUST be
maintained above 130°F.
Dropping below 130°F will
cause acidic condensate to
form within the appliance’s heat
exchanger and damage the
copper finned-tubes.
NOTICE!
NOTICE!
This appliance is furnished with a 3/4” drain
pipe which is used to drain built-up
condensation inside the combustion
chamber. Connect this 3/4” drain pipe to
the common drain piping.
Most installation codes require a 3/4”
manual drain (ball) valve to be installed at
the lowest point on the heat exchanger.
Make sure the appliance is isolated from the
heating system before using the manual
drain valve.
Revised: May 19, 2016
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3.2.2 Appliance Connections (1500, 1700 & 2000 Sizes)
All connections must be in compliance with national, state, and local code requirements.
NOTICE!
This is a non-condensing gas-fired
appliance and the incoming (return)
water temperature MUST be
maintained above 130°F. Dropping
below 130°F will cause acidic
condensate to form within the
appliance’s heat exchanger and
damage the copper finned-tubes.
NOTICE!
NOTICE!
This appliance is furnished with a 3/4” drain
pipe which is used to drain built-up
condensation inside the combustion
chamber. Connect this 3/4” drain pipe to
the common drain piping.
Most installation codes require a 3/4”
manual drain (ball) valve to be installed at
the lowest point on the heat exchanger.
Make sure the appliance is isolated from the
heating system before using the manual
drain valve.
Revised: May 19, 2016
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3.2.3 Appliance Connections (N2500-MFD & N3000-MFD)
All connections must be in compliance with national, state, and local code requirements.
NOTICE!
This is a non-condensing gas-fired
appliance and the incoming (return)
water temperature MUST be
maintained above 130°F. Dropping
below 130°F will cause acidic
condensate to form within the
appliance’s heat exchanger and
damage the copper finned-tubes.
NOTICE!
This appliance is furnished with a 3/4” drain
pipe which is used to drain built-up
condensation inside the combustion
chamber. Connect this 3/4” drain pipe to
the common drain piping.
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
NOTICE!
The appliance is furnished with a 3/4”
manual drain (ball) valve which allows the
user to completely drain the heat
exchanger. Make sure the appliance is
isolated from the heating system before
using the manual drain valve.
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3.3 Electrical Connections
3.3.1 Power Requirements
The MFD and VELOX series boilers and water heaters require 208-240 VAC, single phase, 60 hertz
electrical service. The MCA and MOCP are indicated on the appliance’s rating nameplate. Before
starting the appliance, check to ensure that the proper electrical service is connected to the appliance.
750 – 1000
1500 – 1700 – 2000
2500 – 3000
Maximum Over-Current
Protection
5 Amps
10 Amps
15 Amps
Recommended Circuit
Capacity
10 Amps
15 Amps
20 Amps
An external electrical disconnect and overload
protection (not supplied with the appliance) are
required. Refer to Section 6.1 for proper wiring
and configuration of the electrical connections.
The electrical service must be installed and
grounded in accordance with local codes or in
the absence of such requirements, in the U.S.
with National Electrical Codes, ANSI/NFPA No.
70 latest edition or, in Canada, to the current
Canadian Electrical Code, Part I, CSA C22.1
latest edition. Installed conduit must not block
any of the appliance’s openings and must allow
the front door to be opened.
The low voltage (TB1) and high voltage (TB2)
terminal blocks are located inside the junction
box, located on the right rear surface of the
appliance as shown to the right:
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
Electrical Junction Box:
Low Voltage (TB1) &
High Voltage (TB2)
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3.3.2 High Voltage (TB2) Terminal Block
Refer to Section 6.1 for a detailed drawing of the electrical junction
box on the rear surface of the appliance. An image of the high voltage
(TB2) terminal block and descriptions of each of the terminals are
provided below:
Be sure to check the
nameplate on the
appliance before
connecting the electrical
supply.
L1 208-240V – Connect the 1st hot lead of the 208-240VAC, single
phase, 60Hz electrical service to the TB2-1 terminal.
NOTICE!
A dedicated earth ground
(green wire) is required to
avoid nuisance shutdowns. Do
not ground through the conduit!
The high voltage (TB2)
terminal block on the MFD
and VELOX boilers & water
heaters with NURO controls
requires two hot leads (L1 &
L2), two neutrals (N), and a
ground lead (G) for 208-240
VAC, single phase 60Hz
electrical supply. This
terminal block (TB2) also
contains dry-contact relays
with a maximum voltage
rating of 240VAC and 1/2
Amp maximum current
capacity. Incorrect wiring can
result in equipment damage,
injury, or death.
L2 208-240V – Connect the 2nd hot lead of the 208-240VAC, single
phase, 60Hz electrical service to the TB2-2 terminal.
NEUTRAL 208-240V – Connect the neutral lead(s) of the 208240VAC, single phase, 60Hz electrical service to the TB2-3 & TB2-4
terminals.
GROUND G1 – Connect the ground lead from the electrical service to
the TB2-5 terminal.
Start Interlock #2 – The Start Interlock #2 TB2-6 & TB2-7 terminals
are in series with Start Interlock #1 and provide additional connection
points for auxiliary safety devices. This circuit is energized with
120VAC, so the contacts on any auxiliary safety devices must be rated
for minimum 120VAC.
Start Interlock #1 – The Start Interlock #1 TB2-8 & TB2-9 terminals
can be used for auxiliary safety devices such as damper limit switches,
control valve limit switches, emergency stop buttons, and low water
cutoff devices. This circuit is energized with 120VAC, so the contacts
on any auxiliary safety devices must be rated for a minimum of
120VAC. The appliance ships with a factory-installed jumper across
Start Interlock #1 and Start Interlock #2 terminals. Remove the
jumper(s) if using any auxiliary safety devices.
NOTE: The Start Interlock circuit must close within 5 minutes of a call for heat. Failure to
close the Start Interlock circuit will cause the appliance to lockout on alarm.
Revised: May 19, 2016
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Low Water Cutoff – Connect the common (COM) and normally-open (NO) terminals from an auxiliary
low water cutoff device to the TB2-10 & TB2-11 terminals. This circuit is energized with 120VAC, so
the contacts on the auxiliary low water cutoff device must be rated for a minimum of 120VAC.
Auxiliary Input – The TB2-12 & TB2-13 terminals are reserved for future use. This circuit is energized
with 120VAC.
Air Damper Interlock – The Air Damper Interlock TB2-14 & TB2-15 terminals allow for proof of open
end limit switch on a motorized air damper. This circuit is energized with 120VAC, so the contacts on the
end limit switch must be rated for minimum 120VAC. The appliance ships with a factory-installed
jumper across the Air Damper Interlock terminals. Remove the jumper if connecting a motorized air
damper with end limit switch.
Ground – Grounding connection for auxiliary safety/limit devices on terminal TB2-16.
NOTE: This ground terminal is connected to the TB2 sheet metal and is not common with the
appliance’s electrical service ground.
Relay A – User-configurable relay output #1 located on terminals TB2-23 & TB2-24. The normally-open
contacts on this relay have a maximum voltage rating of 240VAC and maximum capacity of 1/2 Amp.
Relay B – User-configurable relay output #2 located on terminals TB2-21 & TB2-22. The normally-open
contacts on this relay have a maximum voltage rating of 240VAC and maximum capacity of 1/2 Amp.
Relay C – User-configurable relay output #3 located on terminals TB2-19 & TB2-20. The normally-open
contacts on this relay have a maximum voltage rating of 240VAC and maximum capacity of 1/2 Amp.
Relay D – User-configurable relay output #4 located on terminals TB2-17 & TB2-18. The normally-open
contacts on this relay have a maximum voltage rating of 240VAC and maximum capacity of 1/2 Amp.
NOTE: Refer to Section 6.1 for proper wiring and configuration of the electrical connections.
Relays A through C can be user-configured through the NURO touch screen interface to
control devices such the Comfort Heat (CH) Pump, Domestic Hot Water (DHW) Pump, Air
Damper, System Pump, etc. Relay D cannot be used for Air Damper.
Master Alarm Relay – The Master Alarm Relay TB2-25 & TB2-26 terminals are normally-open dry
contacts that close in the event of an alarm output from the NURO control. The normally-open contacts
on this relay have a maximum voltage rating of 240VAC and maximum current capacity of 1/2 Amp.
NOTE: The two 24VAC transformers in the control panel cannot be used to power any other
devices. They are dedicated to the NURO and SOLA only.
Revised: May 19, 2016
Release May 17, 2016
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3.3.3 Low Voltage (TB1) Terminal Block
Refer to Section 6.1 for a detailed drawing of the electrical junction box on the rear surface of the
appliance. An image of the low voltage (TB1) terminal block and descriptions of each of the terminals
are provided below:
Enable/Disable –TB1-1 and TB1-2 can be used to remotely enable or disable the appliance. The
functionality of these terminals is user-configurable through the NURO controls, but generally closure of
the Enable/Disable circuit provides a call for heat to the appliance. Opening this circuit prevents the
appliance from running.
The appliance ships with a factory-installed jumper across the Enable/Disable terminals. This circuit is
energized with a 24VAC potential, so the contacts on any remote enable devices must be rated for
minimum 24VAC.
4-20mA Analog Input – TB1-3 and TB1-4 can be used to provide a remote analog 4-20mA control
signal to the appliance. This analog signal can be used to change the appliance’s operating setpoint or
firing rate.
Spare Analog Input – TB1-5 and TB1-6 are reserved for future use.
HDR Temp Sensor – TB1-7 and TB1-8 can be used to connect a remote header temperature sensor,
installed in the primary hydronic system piping, downstream of all the appliances. This temperature
sensor must be a 2-wire 12kΩ NTC thermistor. This circuit is energized by the appliance with a 5VDC
potential.
DHW Stat/Sensor – TB1-9 and TB1-10 can be used to connect either an aquastat or remote DHW
temperature sensor installed in a domestic hot water storage tank. If using an aquastat, use a SPST
normally-closed, break on rise type with either a fixed or adjustable deadband above and below the
setpoint.
Alternatively, if using a temperature sensor, it must be a 2-wire 12kΩ NTC thermistor and be of
sufficient length to measure an accurate storage tank temperature. This circuit is energized by the
appliance with a 5VDC potential.
Revised: May 19, 2016
Release May 17, 2016
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Outdoor Temp Sensor – TB1-11 and TB1-12 can be used to connect an outdoor air temperature sensor
which allows the NURO control to be programmed to run an outdoor air schedule. The outdoor air
temperature sensor must be a 2-wire 12kΩ NTC thermistor and should be installed on the North face of
the building and shielded from direct sunlight exposure. This circuit is energized by the appliance with a
5VDC potential.
Night Setback – TB1-13 and TB1-14 can be used to connect a day/night or occupancy timer. Closure of
the Night Setback circuit enables the Night Setback mode which reduces the appliance’s operating
setpoint. Opening this circuit resumes normal operation. This circuit is energized by the appliance with
a 5VDC potential, so the contacts on the day/night timer must be rated for minimum 5VDC.
4-20mA Analog Output – TB1-15 and TB1-16 provide a 4-20mA analog output signal which tracks the
appliance’s firing rate. When operating at full power (maximum firing rate), the appliance will provide a
20mA output (adjustable). When operating at minimum power (minimum firing rate), the appliance will
provide a 4mA output (adjustable). See NURO Boiler Controller: Advanced User’s Guide for additional
instructions on adjusting the analog output signals.
Ground – TB1-17 provides an equipment (frame) ground connection for input, output, or communication
connections. For independently powered control devices, it may be necessary to create a common
ground.
Cascade Shield & Cascade – TB1-18, TB1-19, and TB1-20 can be used to setup a cascade system with
multiple MFD or VELOX appliances with NURO controls. Terminals TB1-19 and TB1-20 are reserved for
the cascade communication between the master and member positions. Terminal TB1-18 should be
used to connect the cascade communication wiring shield between all appliances. The cascade and
shielding must be wired from the master appliance to each individual member appliance in a daisychain fashion.
NOTE: Only ground the shield at the master boiler or water heater.
MODBUS COM & MODBUS Shield – TB1-22, TB1-23, and TB1-24 can be used to integrate the
appliance with a Building Management System (BMS), Protocol Converter, or other device capable of
RS-485 2-wire MODBUS communication. Terminals TB1-22 and TB1-23 are reserved for MODBUS and
terminal TB1-18 provides a connection for the MODBUS communication wire shield.
NOTE: Only ground the shield at the master boiler or water heater.
ECOM 1, 2, & 3 – TB1-25, TB1-26, and TB1-27 can be used to connect a wireless outdoor air
temperature sensor. The wireless receiver should be installed at or near the appliance, and the wireless
temperature sensor should be installed on the North face of the building and shielded from direct
sunlight exposure.
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
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3.4 Combustion Air
3.4.1 Air Inlet Requirements – United States
Air inlet requirements for the United States are established by NFPA 54/ANSI Z223.1 & NFPA/ANSI
211. When air is supplied from inside the building, the total required volume shall be the sum of the
required volume for all the appliances located in the mechanical room. Adjacent rooms furnished with
fixed openings communicating directly with the mechanical room are considered part of the required
volume. The minimum volume is 50 ft3 per 1,000 Btu/hr (4.8 m3/kW) of installed appliance input capacity.
Openings used to connect indoor spaces to obtain the required minimum volume shall be sized as
follows:

When rooms are on the same floor, each opening shall have an area equal to 1 square inch for
each 1,000 Btu/hr (2,200 mm2/kW) of installed appliance input capacity, but not less than 100
square inches. One opening should commence less than 12 inches above the floor and the other
less than 12 inches below the ceiling. The minimum dimension of air openings shall be 3 inches.

When rooms are on different floors, each opening shall have an area equal to 2 square inches for
each 1,000 Btu/hr (4,400 mm2/kW) of installed appliance input capacity.
When combustion air is supplied from outside the building, the mechanical room shall be provided with
one or two openings to ensure adequate combustion air and proper ventilation.
When using one permanent opening, the opening shall commence within 12 inches of the ceiling and
shall communicate directly with the outdoors or through a vertical or horizontal duct that communicates
to the outdoors.
Under no circumstances
shall the mechanical room
ever be under a negative
pressure.
Particular care should be
taken when exhaust fans,
compressors, air-handling
units, or other equipment
may rob air from the boiler.
Note that this equipment
might be in rooms other
than the boiler room. This
applies to both sealed
combustion and
atmospheric room
combustion air applications.
NOTES:
When using two permanent openings, one opening shall commence
within 12 inches above the floor and the other within 12 inches below the
ceiling, preferably on opposite walls. The openings shall communicate
directly, or by way of ducts, with free outdoor air. The minimum net free
area of the openings shall be calculated in accordance with the following:

When air is taken directly from outside the building, each
opening (minimum of two, as outlined above), 1 square inch for
each 4,000 Btu/hr (550 mm2/kW) of total appliance input is
required.

When air is taken from the outdoors through a vertical duct into
the mechanical room, 1 square inch per 4,000 Btu/hr (550
mm2/kW) of total appliance input is required.

When air is taken from the outdoors through a horizontal duct
into the mechanical room, 1 square inch per 2,000 Btu/hr (1,100
mm2/kW) of total appliance input is required.
1. The required size of openings for combustion and ventilation air shall be based
on the net free area of the opening.
2. Screens shall be not smaller than 1/4 inch.
3. Motorized louvers shall be interlocked with the appliance so that they are
proven open prior to main burner ignition and operation.
Revised: May 19, 2016
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United States Minimum Area of Ventilation Openings per Appliance (Sq In)
Appliance Size
(BTU/Hr)
750,000
1,000,000
1,500,000
1,700,000
2,000,000
2,500,000
3,000,000
INDOOR AIR SUPPLY
SAME
FLOOR
DIFF
FLOORS
750
1000
1500
1700
2000
2500
3000
1500
2000
3000
3400
4000
5000
6000
AIR SOURCE
OUTDOOR AIR SUPPLY
TWO OPENINGS
ONE
VERT
HORIZ
OPENING
DIRECT
DUCT
DUCT
250
188
188
375
334
250
250
500
500
375
375
750
567
425
425
850
667
500
500
1000
834
625
625
1250
1000
750
750
1500
3.4.2 Air Inlet Requirements - Canada
Air inlet requirements for the Canadian Provinces are established by CAN/CSA B149.1. Ventilation of
the space occupied by fuel burning appliance(s) or equipment shall be supplied by a ventilation opening
at the highest practicable point communicating with the outdoors. The total cross sectional area of the
ventilation opening must be either 10% of the net free area required for combustion air or 10 sq. in.
(6,500 mm2), whichever is greater.
1. The free area of a combustion air supply opening is calculated by deducting
the blockage area of any fixed louvers, grilles or screens from the total area
of the opening.
NOTES:
2. Screens shall be not smaller than 1/4 inch.
3. Motorized louvers shall be interlocked with the appliance so that they are
proven open prior to main burner ignition and operation.
A. Ventilation of the space occupied by fuel burning appliance(s) or equipment shall be supplied by a
ventilation opening at the highest practicable point communicating with the outdoors. The total cross
sectional area of the ventilation opening must be either 10% of the net free area required for
combustion air or 10 sq. in. (6,500 mm2), whichever is greater.
B. Use the following opening calculation for MFD and VELOX boilers and water heaters:
When combustion air is supplied for a forced draft burner by natural airflow from the outdoors
and there is no draft regulator or draft hood in the same space, there shall be a permanent
opening with a cross sectional area not less than 1 sq. in/30,000 Btu/Hr (70 mm2/kW) of the
total rated input to the burner(s). This opening must not interfere with the ventilation air opening
defined in Paragraph A.
C. Use the following opening calculation for MFD and VELOX boilers and water heaters or other
natural draft or fan-assist appliances:
When combustion air is supplied for natural or fan-assisted burners by natural airflow from the
outdoors, there shall be a permanent opening with a cross sectional area not less than 1 sq.
in/7,000 Btu/Hr (321 mm2/kW) up to and including 1,000,000 Btu/Hr plus 1 sq. in./14,000 Btu/Hr
(155 mm2/kW) in excess of 1,000,000 Btu/Hr. This opening must be either located at or ducted
to a point not more than 18 in. (450 mm) or less than 6 inches (150 mm) above floor level. This
opening is in addition to the ventilation air opening defined in Paragraph A.
Revised: May 19, 2016
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D. When combustion air is supplied by natural airflow into a space containing both types of appliances
described in Paragraphs B and C, the cross sectional area of the opening shall not be less than
the sum of the cross sectional areas for all appliances in the space as calculated by the applicable
method. This opening is in addition to the ventilation air opening defined in Paragraph A.
E. When a duct is used to meet the requirement for combustion air supply, as described in
Paragraphs A through D above, the opening of the duct shall be located so there is no possibility
of cold air affecting steam or water piping, electrical equipment, or mechanical equipment.
F. When combustion air is supplied by mechanical means, an airflow-sensing device must be
installed. It must be wired into the pre-ignition limit interlock circuit to prevent the burner from
starting or to stop an operating burner in case of air supply failure.
G. When all combustion air is supplied through a make-up air heater, and the appliance is interlocked
to the heater, the requirements of Paragraphs A through F do not apply.
Canadian Minimum Area of Combustion and Ventilation Air Openings
Appliance Size
(BTU/Hr)
750,000
1,000,000
1,500,000
1,700,000
2,000,000
2,500,000
3,000,000
Required Combustion Air
Opening
Ventilation Air Opening
in2
mm2
in2
mm2
25
33.3
50
57
67
83.3
100
16,129
24,484
32,258
36,774
43,225
53,742
64,516
10
10
10
10
10
10
10
6,452
6,452
6,452
6,452
6,452
6,452
6,452
3.4.3 MFD & VELOX Combustion Air Requirements
The table below summarizes the combustion air requirements for MFD & VELOX appliances:
MFD
Boiler
VELOX
Boiler
MFD
Water Heater
VELOX
Water Heater
Air Intake
Connection
Required SCFM
Combustion Air
N750-MFD
N750-VX
W750-MFD
W750-VX
8”
188
N1000-MFD
N1000-VX
W1000-MFD
W1000-VX
8”
251
N1500-MFD
N1500-VX
W1500-MFD
W1500-VX
8”
364
-
N1700-VX
-
W1700-VX
8”
413
N2000-MFD
N2000-VX
W2000-MFD
W2000-VX
8”
501
N2500-MFD
-
-
-
12” x 12”
583
N3000-MFD
-
-
-
12” x 12”
700
N2500-MFD*
-
-
-
10”
583
N3000-MFD*
-
-
-
10”
700
*With optional air intake adapter (part # 23-0000-0480) installed for a 10” circular connection.
Revised: May 19, 2016
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3.4.4 Direct Vent / Sealed Combustion Installations
The MFD and VELOX series boilers and water heaters are certified for operation in direct vent / sealed
combustion systems, which feature combustion air intake ductwork which sources the combustion air
supply from outdoors. The flow of combustion air through this ductwork is maintained by the
appliance’s internal combustion blower.
The combustion air intake ductwork can be constructed with PVC, CPVC, single wall galvanized steel,
or other suitable materials. The ductwork must be rigid enough to maintain the full required cross
sectional area under all operating conditions.
NOTE: The combustion air intake ductwork must be sufficiently rigid in order to prevent
collapse due to the potential for negative pressures inside the ductwork. If the ductwork
collapses, this will restrict the combustion air supply to the appliance which may prohibit
operation.
Proper sealing of the combustion air intake ductwork is necessary to prevent infiltration of air from
conditioned space. For example, joints in PVC or CPVC piping must be cemented. For galvanized
duct, wrap each joint and seam with adhesive aluminum tape or other sealant. Harsco Industrial
Patterson-Kelley recommends installing a 1” x 1” or larger bird screen on the exterior termination.
Ensure that the screen does not become blocked with snow, ice, insects etc.
The combustion air supply must be free from dust, lint, etc. The presence of such materials in the air
supplied to the burner could cause nuisance "Low Air" shutdowns or premature burner failure. The
appliance should not be operated during construction while the possibility of drywall dust, demolition
dust, etc. exists.
The combustion air supply must be completely free of chemical fumes which may be corrosive when
burned in the appliance. Common chemicals which must be avoided are fluorocarbons and other
halogenated compounds, most commonly present as refrigerants or solvents, such as Freon®,
trichloroethylene, perchloroethylene, chlorine, etc. These chemicals, when burned, cause improper
combustion and premature appliance failure due to the formation of acids which quickly attack the heat
exchanger and the flue piping materials.
Revised: May 19, 2016
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Sizing the Combustion Air Intake Ductwork
The combustion air flow rate requirements per appliance model are summarized in Section 3.4.3.
When sizing the combustion air intake ductwork, the pressure drop through this ductwork MUST NOT
exceed 0.5” W.C. as described in the table below:
Total
Allowable
Pressure Drop
/Friction Loss
Maximum
Allowable Pressure
Drop through
Combustion Air
Duct
Allowable Vent
Pressure
750/1000/1500/1700/2000 VELOX
Category I
N/A
0.5” W.C.
-.01” W.C. to -0.05”
W.C.
750/1000/1500/1700/2000 MFD
Category II
N/A
0.5” W.C.
-.01” W.C. to -0.05”
W.C.
N/A
0.5” W.C.
-.01” W.C. to -0.05”
W.C.
1.5” W.C.
0.5” W.C.
+0.01” W.C. to +1.0”
W.C.
1.0” W.C
0.5” W.C.
+0.01” W.C. to +0.5”
W.C.
Appliance Size
2500/3000 MFD Category II
750/1000/1500/1700/2000 MFD
Category IV
2500/3000 MFD
Category IV
NOTE: If the combustion air intake ductwork and the exhaust vent terminate on the same wall of
the building, they must utilize the same type of termination fitting.
NOTE: Harsco Industrial Patterson-Kelley recommends including a motorized combustion air
damper in each appliance’s air intake ductwork. Proceed to Section 3.4.5 for more information.
Revised: May 19, 2016
Release May 17, 2016
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3.4.5 Motorized Combustion Air Dampers
Harsco Industrial Patterson-Kelley recommends, and most installation codes require, the use of
motorized combustion air dampers with end limit switches installed in the combustion air intake
ductwork upstream of each appliance. This damper isolates the combustion air supply when the
appliance is in standby. Once the appliance receives a call for heat, the motorized combustion air
damper opens and the end limit switch must close before the appliance can proceed to ignition. Harsco
Industrial Patterson-Kelley offers motorized combustion air dampers with built-in end limits switches for
sale, which are summarized in the table below:
Table of Recommended Motorized Combustion Air Dampers
Combustion Air Ductwork
Size
8”
Normally-Closed
Motorized Damper
A
B
C
D
10-0490-6944
8”
8”
11”
2.38”
10”
10-0490-6945
10”
10”
13”
3.38”
12”
10-0490-6946
12”
12”
15”
4.38”
14”
10-0490-6989
14”
14”
17”
5.5”
These normally-closed motorized combustion air dampers operate on 120 VAC and feature a built in
end limit switch which must be wired to the appliances’ Air Damper Interlock circuit (terminals TB2-13 &
TB2-14). Upon a call for heat, the appliances’ Air Damper Relay energizes, which drives the damper
motor open. Once the damper reaches the fully-open position, the end limit switch makes contact and
closes the Air Damper Interlock circuit, allowing the appliance to proceed to ignition. The diagram
below shows the wiring necessary to install the normally-closed motorized damper.
NOTE: The power source to drive the damper actuator motor must be provided externally. The
appliance DOES NOT provide a power source for this purpose.
NOTE: Combustion air dampers other than those listed in the table above may require voltages
other than 120VAC. This is acceptable, provided the required voltage does not exceed
240VAC.
NOTE: The Air Damper Interlock circuit for the end limit switch is always 120VAC which is
sourced from the appliance itself. All end limit switches must be rated for 120VAC.
Revised: May 19, 2016
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For correct installation of a
vent system, read all of these
instructions and refer to the
vent manufacturer’s
instructions.
Failure to use a proper vent
system (types and materials)
as described in this manual
will void the appliance
warranty and may result in
rapid deterioration of the
venting system, creating a
health or life safety hazard.
Faulty vent installation can
allow toxic fumes to be
released into living areas.
This may cause property
damage, injury, or death
NOTICE!
Motorized combustion air dampers must be powered from an
external power supply other than the appliance. The figure below
shows a sample installation in which Relay C is user-selected to
operate a 120VAC motorized air damper. Relay C is normallyopen, so when the appliance is in standby, the combustion air
damper remains closed. Once a call for heat is received, Relay C
closes the 120VAC circuit (external power supply) which provides
power to the damper motor, opening the damper.
Once the motorized damper is fully-open, its end limit switch
completes the Air Damper Interlock circuit (120VAC) which allows
the appliance to proceed to ignition.
External power supplies are required for Relay A, Relay B, Relay C
and Relay D. Because power is provided from an external source,
the power is still present when the appliance is turned off. Check
all voltage sources have been disconnected prior to servicing.
Failure to do so could result in electrocution, injury, or death.
FUSED
Relay A, Relay B,
Relay C, and Relay
D are rated for a
maximum voltage of
240VAC and a
maximum current
capacity of 1/2 Amp.
Customer must
supply fusing for all
current connected to
the relays.
Connecting a
motorized damper
which exceeds the
voltage or current
capacity of the relay
could cause
permanent damage
to the relay.
NOTE: The NURO control allows the user to allocate Relay A, B, or C for use with a motorized
combustion air damper. The figure above shows Relay C in use for the motorized
combustion air damper. Depending on the user-configuration, Relay A, Relay B, or
Relay C can be selected to operate the combustion air damper.
Revised: May 19, 2016
Release May 17, 2016
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3.5 Flue Gas / Exhaust Venting
All vent installations shall be in accordance with NFPA 54/ANSI Z223.1, the National Fuel Gas Code, or
CAN/CSA-B149.1, the Natural Gas and Propane Installation Code, or applicable provisions of the local
building codes.
The vent material to be used for US and Canada is listed in the Table of Acceptable Materials for
Venting Systems located in Section 2.5.5.
For interior clearance requirements, refer to Section 2.5.6. The vent shall extend at least three (3) feet
above the roof, or at least two (2) feet above the highest part of any structure within ten (10) feet of the
vent. Refer to Section 3.5.2 and Section 3.5.4 for an illustration of the flue termination. Additionally
the boiler vent shall terminate at least three (3) feet above a forced air inlet located within ten (10) feet.
To prevent the possible re-circulation of flue gases, the vent designer must take into consideration such
things as prevailing winds, eddy zones, building configurations, etc. Harsco Industrial, PattersonKelley cannot be responsible for the effects such adverse conditions may have on the operation
of the appliances.
Vertical vents are allowed to be terminated with a variety of ends, including plain straight pipe, elbow, or
vent tee. Horizontal vents must be terminated with an elbow or vent tee. Similarly a bird screen with 1” x
1” openings is recommended for termination. Harsco Industrial, Patterson-Kelley does not recommend
using a vent rain cap of any type.
VELOX Series Boilers & Water Heaters (Category I Venting)
VELOX series boilers are Category I appliances, as defined in ANSI Z21.13/CSA 4.9, latest edition and
are suitable for use with Type “B” vents. VELOX series water heaters are also Category I appliances,
as defined in ANSI Z21.10.3/CSA 4.3, latest edition and are suitable for use with Type “B” vents. The
VELOX series boilers and water heaters are designed to operate under a slight negative exhaust
pressure. It is critical to ensure the flue venting material is certified for Category I operation and is
suitable for use with the VELOX appliance. Refer to Section 3.5.1 for more information on Category I
vent installations.
NOTE: For Category I installations, ensure the flue venting system is designed to maintain a
slightly negative exhaust pressure between -0.01” W.C. and -0.05” W.C.
MODU-FIRE Forced Draft Boilers & Water Heaters (Category II or IV Venting)
MODU-FIRE Forced-Draft series boilers are dual-certified as Category II or IV appliances, as defined
in ANSI Z21.13/CSA 4.9, latest edition. MODU-FIRE Forced-Draft series water heaters are also dualcertified as Category II or IV appliances, as defined in ANSI Z21.10.3/CSA 4.3, latest edition. The
MFD series boilers and water heaters are capable of operating with slightly negative to slightly positive
exhaust pressure. It is critical to ensure the flue vent material is certified for Category II or IV operation
and is suitable for use with the MFD appliance. Refer to Section 3.5.3 for more information on
Category II/IV vent installations.
NOTE: For Category II installations, ensure the flue venting system is designed to maintain a
slightly negative exhaust pressure which MUST NOT exceed -0.05” W.C.
NOTE: For Category IV installations, ensure the flue venting system is designed to maintain
a slightly positive pressure which MUST BE in the following ranges:
 +0.01” W.C. and +1.5” W.C. (MFD Sizes 750 through 2000)
 +0.01” W.C. and +1.0” W.C. (MFD Sizes 2500 & 3000).
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
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3.5.1 Category I Vent Installation (VELOX Boilers and Water Heaters Only)
VELOX series boilers are Category I appliances, as defined in ANSI Z21.13/CSA 4.9, latest edition and
VELOX series water heaters are also Category I appliances, as defined in ANSI Z21.10.3/CSA 4.3,
latest edition. Theses appliances are suitable for use with Type “B” vent and operate with a nonpositive vent static pressure and with an elevated flue gas temperature that is unlikely to produce
excessive condensation in the vent. For Category I installations, Patterson-Kelley recommends
increasing the vent pipe size at least one size above the appliance’s exhaust vent connection.
VELOX
Boiler
VELOX
Water Heater
Air Intake
Connection
Exhaust Vent
Connection
Minimum Recommended
Category I Vent Pipe Size
N750-VX
W750-VX
8”
6”
8”
N1000-VX
W1000-VX
8”
6”
8”
N1500-VX
W1500-VX
8”
8”
10”
N1700-VX
W1700-VX
8”
8”
10”
N2000-VX
W2000-VX
8”
8”
10”
The appliance vent should not be connected into any portion of another
mechanical draft system without consulting the vent manufacturer. The
appliance shall not be connected to any part of a vent system serving a
Category II, III, or IV appliance, nor shall a Category II, III, or IV appliance be
connected to any part of a vent system serving this appliance. Improper
interconnection of venting systems may cause leakage of flue gases into
occupied spaces. This can cause serious injury or death.
NOTE: For Category I installations, ensure the flue venting system is designed to maintain
a slightly negative vent pressure between -0.01” W.C. and -0.05” W.C.
NOTE: For Category I installations, NEVER decrease the size of the vent piping below the
nominal exhaust vent connection from the appliance.
The connection from the appliance to the vent should be as direct as possible and the upward slope of
any horizontal breaching should be at least 1/4 inch per linear foot. Support the venting system in
accordance with the manufacturer’s instructions. The vent connection on the appliance itself shall not
be used to support the weight of the venting system.
Barometric Dampers (Category I Installations Only)
While not required in all installations, one effective method of controlling the draft in Category I
applications is to install a barometric damper in the flue vent piping downstream of the appliance.
Barometric dampers help regulate a consistent (negative) vent pressure in the flue vent piping. Harsco
Industrial Patterson-Kelley offers barometric dampers for purchase:
 10” Barometric Damper = Part # 86-2290-0200
 12” Barometric Damper = Part # 86-2290-0250
Direct Vent / Sealed Combustion
If the Category I installation is direct vent / sealed combustion, then a normally-closed motorized
damper is required on the combustion air intake ductwork. Refer to Section 3.4.4 for more information.
Revised: May 19, 2016
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3.5.2 VELOX Boilers & Water Heaters: Acceptable Category I Vent Configurations
VELOX Category I: Through-the-roof (exhaust only)
Minimum flue vent clearance:
36” above nearby parapet wall
12” above expected snowline
Acceptable termination: B-vent
with non-restrictive rain cap
(shown)
Condensate drain
(stainless steel or
hi-temp silicone
tubing)
4” loop/trap for condensate or rain
water disposal (pipe to drain)
Acceptable locations for barometric
damper (only one needed)
NOTE: For Category I installations, ensure the flue venting system is designed to maintain a
slightly negative exhaust pressure which MUST NOT exceed -0.05” W.C.
Revised: May 19, 2016
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VELOX Category I: Through-the-roof (sealed combustion)
Acceptable termination: B-vent
with non-restrictive rain cap
(shown)
Minimum air intake clearance:
12” above expected snowline
Minimum flue vent clearance:
36” above air intake
Motorized combustion
air damper
Condensate drain
(stainless steel or
hi-temp silicone
tubing)
Acceptable locations for barometric
damper (only use one damper)
4” loop/trap for condensate or rain
water disposal (pipe to drain)
NOTE: For Category I installations, ensure the flue venting system is designed to maintain a
slightly negative exhaust pressure between -0.01” W.C. and -0.05” W.C.
NOTE: For Category I sealed combustion installations, ensure the combustion air ductwork is
designed for a maximum frictional loss of -0.5” W.C.
NOTE: A motorized combustion air damper is required in the combustion air ductwork in all
sealed combustion applications.
Revised: May 19, 2016
Release May 17, 2016
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3.5.3 Category II or IV Vent Installation (MFD Boilers and Water Heaters Only)
MODU-FIRE Forced-Draft series boilers are dual certified as Category II or IV appliances, as defined
in ANSI Z21.13/CSA 4.9, latest edition and are not suitable for use with Type “B” Vents. MODU-FIRE
Forced-Draft series water heaters are also dual-certified as Category II or IV appliances, as defined in
ANSI Z21.10.3/CSA 4.3, latest edition and are not suitable for use with Type “B” vents.
MFD
Boiler
MFD
Water Heater
Air Intake
Connection
Exhaust Vent
Connection
Minimum Recommended
Category II/IV Vent Pipe Size
N750-MFD
W750-MFD
8”
6”
5”
N1000-MFD
W1000-MFD
8”
6”
5”
N1500-MFD
W1500-MFD
8”
8”
6”
N2000-MFD
W2000-MFD
8”
8”
6”
N2500-MFD
12” x 12”
10”
8”
N3000-MFD
12” x 12”
10”
8”
N2500-MFD*
10”
10”
8”
N3000-MFD*
10”
10”
8”
*With optional air intake adapter (part # 23-0000-0480) installed for a 10” circular connection.
The appliance vent should not be connected into any portion of another
mechanical draft system without consulting the vent manufacturer. The
appliance shall not be connected to any part of a vent system serving a
Category I or III appliance, nor shall a Category I or III appliance be
connected to any part of the vent system serving this appliance. Improper
interconnection of venting systems may cause leakage of flue gases into
occupied spaces. This can cause serious injury or death.
Do not use a barometric damper if operating with a positive stack pressure
(Category IV). Harmful flue gases may leak into the room which can cause
serious injury or death.
NOTE: For Category II installations, ensure the flue venting system is designed to maintain a
slightly negative exhaust pressure between -0.01” W.C. and -0.05” W.C.
NOTE: For Category IV installations, ensure the flue venting system is designed to maintain
a slightly positive exhaust pressure which MUST BE in the following ranges:
 +0.01” W.C. and +1.5” W.C. (MFD Sizes 750 through 2000)
 +0.01” W.C. and +1.0” W.C. (MFD Sizes 2500 & 3000).
The connection from the appliance to the vent should be as direct as possible and the upward slope of
any horizontal breaching should be at least 1/4 inch per linear foot.
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
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1004905935 P-K MFD & VELOX 750-3000
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Category IV Installations
If the vent installation is designed for Category IV conditions only (condensing – positive pressure) as it
is defined in ANSI Z21.13/CSA 4.9, latest edition, the installations shall be in accordance with NFPA
54/ANSI Z223.1, the National Fuel Gas Code, or CAN/CSA-B149.1, the Natural Gas and Propane
Installation Code, or applicable provisions of the local building codes.
The following materials are used by venting manufacturers to produce listed venting systems.

AL29-4C Stainless Steel Vent Systems listed and labeled to UL1738 Venting Systems for GasBurning Appliances, Categories II, III, and IV

316L Stainless Steel where certified and warranted by the vent manufacturer for venting of
Category II, III or IV appliances
These prefabricated venting systems must be installed according to the manufacturer’s installation
instructions. Special care should be taken to ensure that any and all integral gasketing is properly
assembled and creates a gas and water tight seal. Systems that require silicone caulking for gasketing
should only be installed with silicone caulk that is recommended by the vent manufacturer, or if none is
recommended, only high temperature, waterproof, silicone caulk should be used. Support of the
venting system must be according to the manufacturer’s instructions. The vent connection on the
appliance itself shall not be used to support the weight of the vent.
Direct Vent / Sealed Combustion
If the Category II or IV installation is direct vent / sealed combustion, then a normally-closed motorized
damper is required on the combustion air intake ductwork. Refer to Section 3.4.4 for more information.
Revised: May 19, 2016
Release May 17, 2016
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3.5.4 MFD Boilers & Water Heaters: Acceptable Category II/IV Vent Configurations
MFD Category II/IV:
Through-the-roof (exhaust only)
MFD Category II/IV:
Sidewall (exhaust only)
Acceptable termination fittings:
 Downward elbow (shown left)
 Horizontal tee (shown right)
 Velocity cone
(1” x 1” bird screen recommended)
Minimum flue vent clearance:
36” above nearby parapet wall
12” above expected snowline
Minimum exhaust
clearance:
12” from sidewall
Condensate drain
(stainless steel or
hi-temp silicone
tubing)
4” loop/trap for condensate or rain
water disposal (pipe to drain)
NOTE: For Category II installations, ensure the flue venting system is designed to maintain a
slightly negative exhaust pressure between -0.01” W.C. and -0.05” W.C.
NOTE: For Category IV installations, ensure the flue venting system is designed to maintain a
slightly positive exhaust pressure which MUST BE in the following ranges:
 +0.01” W.C. and +1.5” W.C. (MFD Sizes 750 through 2000)
 +0.01” W.C. and +1.0” W.C. (MFD Sizes 2500 & 3000).
Revised: May 19, 2016
Release May 17, 2016
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MFD Category II/IV:
Through-the-roof (exhaust only)
MFD Category II/IV:
Sidewall (exhaust only)
Acceptable termination fittings:
 Downward elbow (shown left)
 Horizontal tee (shown right)
 Velocity cone
(1” x 1” bird screen recommended)
Minimum flue vent clearance:
36” above air intake
Motorized combustion
air damper
Minimum
clearance:
12” from sidewall
4” loop/trap for condensate or rain
water disposal (pipe to drain)
Condensate drain
(stainless steel or
hi-temp silicone
tubing)
NOTE: For Category II installations, ensure the flue venting system is designed to maintain a
slightly negative exhaust pressure which does not exceed -0.05” W.C.
NOTE: For Category IV installations, ensure the flue venting system is designed to maintain a
slightly positive exhaust pressure which does not exceed +1.5” W.C. (sizes 750 through 2000)
or +1.0” W.C. (sizes 2500 & 3000).
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
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3.5.5 Venting for Multiple Appliances
While the vent design parameters outlined in Section 3.4 and Section 3.5 still apply, achieving those
same parameters in a combined vent system adds a significant degree of complexity. Therefore,
venting systems for multiple appliances shall be designed by experienced and knowledgeable venting
professionals. The venting system shall be designed to prevent backflow of exhaust gas through idle
appliances. For combined breeching installations, please follow recommendations of a qualified
venting engineer/manufacturer.
Harsco Industrial, Patterson-Kelley recommends that common venting systems be designed for a
maximum continuous exhaust pressure of -0.05” W.C. when measured in the common vent. Locking
inline dampers are recommended on the exhaust connection of each individual appliance in order to
control the exhaust back pressure within the appliance and upstream of this damper. The -0.05” W.C.
in the common flue will also help make sure the exhaust gases from an online appliance does not
backflow through offline appliance(s).
In addition, Harsco Industrial, Patterson-Kelley also recommends the use of motorized combustion air
dampers in the combustion air intake ductwork of each individual appliance. When an appliance is
offline, its combustion air damper will remain closed which will also help prevent the backflow of flue
gases from online appliances. Please refer to Section 3.4.5 for more information.
If the common venting system uses a draft inducer fan or damper device, this
MUST be interlocked with the appliances. In the event this draft inducer
device fails, the interlock circuits to the appliances must be opened in order
to prevent operation. Failure to do so could result in appliance operation
under excessive back pressure conditions which could result in damage to
the appliance and lead to serious injury or death.
The design of any common venting system MUST prevent backflow of
combustion gases through offline boilers or water heaters. Failure to do so
could result in damage to the appliance and lead to serious injury or death.
Revised: May 19, 2016
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3.6 Removing an Existing Boiler or Water Heater
When an existing boiler or water heater is removed from a common venting system, the common
venting system is likely to be too large for proper venting of the appliances remaining connected to it.
At the time of removal of an existing boiler or water heater, while the other appliances remaining
connected to the common venting system are not in operation, the following steps should be followed
with each appliance remaining connected to the common venting system placed in operation:
1. Seal any unused openings in the common venting system.
2. Visually inspect the venting system for proper size and horizontal pitch and determine that there
is no blockage or restriction, leakage, corrosion or other deficiency which could cause an unsafe
condition.
3. Insofar as is practical, close all building doors and windows and all doors between the space in
which the appliance remaining connected to the common venting system are located and other
spaces of the building. Turn on clothes dryers and any appliances not connected to the common
venting system. Turn on any exhaust fans, such as range hoods and bathroom exhausts, so
they will operate at maximum speed. Do not operate a summer exhaust fan. Close fireplace
dampers.
4. Place the appliance being inspected in operation.
Follow the lighting instructions. Adjust the thermostat
so that the appliance will operate continuously.
5. Test for spillage at the draft hood relief opening after 5
minutes of main burner operation. Use the flame of a
match or candle or smoke from a cigarette, cigar or
pipe or smoke pen.
6. After it has been determined that each appliance
remaining connected to the common venting system
properly vents when tested as outlined above, return
doors, windows, exhaust fans, fireplace dampers, and
any other gas-burning appliance to their previous
conditions of use.
Any improper operation of the common venting system
should be corrected so the installation conforms to the
National Fuel Gas Code, ANSI Z223.1 and CSA B149
Installation Code. When resizing any portion of the common
venting system, the common vent system should be resized
to approach the minimum size as determined using the
appropriate tables in part 11 of the National Fuel Gas Code,
ANSI Z223.1/NFPA 54 and/or CAN/CSA B149.1 Natural Gas
and Propane Installation Code.
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
All threaded connections must
be made using a pipe
compound that is resistant to
the action of liquefied
petroleum gases. Do not use
Teflon tape on gas line threads!
NOTICE!
See Pipe Capacity Charts for
Natural Gas or Propane Gas on the
following pages for required pipe
size, based on overall length of pipe
from the meter plus equivalent
length of all fittings. Approximate
sizing may be based on 1 cubic foot
of natural gas per 1,000 Btu per
hour input, i.e., 3,000,000 Btu/hr
requires about 3,000 cubic feet per
hour.
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3.7 Piping
3.7.1 Gas Piping Overview
Before making the gas hook-up, make sure the boiler or water heater is supplied with the type of fuel
shown on the nameplate.
Simplified Gas Piping
The appliance shall be installed such that the gas
ignition system components are protected from
water (dripping, spraying, rain, etc.) during
appliance operation and service (circulator
replacement, control adjustment, etc.)
The appliance is factory fire-tested and adjusted for
proper combustion. The gas train components are
certified to handle a maximum inlet pressure of 14" W.C.
(1/2 psig). Typical gas pressure supply is 7” W.C. for
natural gas and 11" W.C. for propane gas. If the
available gas pressure exceeds 14" W.C., a suitable
additional intermediate gas pressure regulator of the
"lock up" type must be provided to reduce the pressure
to less than 14" W.C. Refer to the table below or the
appliance’s label for the minimum inlet gas pressure.
Natural gas
Propane gas
750 & 1000
3.5” W.C
1500
4” W.C.
7” W.C.
1700 & 2000
3.5” W.C.
2500 & 3000
4” W.C.
N/A
NOTE: When using a vented lock-up gas pressure regulator, the vent piping should be increased
by one pipe size for every 10 equivalent feet of length. Never connect vent piping that is small in
size than the gas regulator’s vent port connection.
Install a sediment trap (drip leg) and a union connection ahead of the primary manual shutoff valve on
the appliance. A gas piping schematic is shown above. Gas piping should be installed in accordance
with National Fuel Gas Code, ANSI Z223.1, latest edition, and any other local codes which may apply; in
Canada see CAN/CSA-B.149.1, latest edition. In the Commonwealth of Massachusetts, the gas cock
must be a “T-handle type.”
Appliance Size (BTU/Hr)
Natural Gas Requirement
(CFH)
Propane Gas Requirement
(CFH)
750,000
750
295
1,000,000
1000
394
1,500,000
1500
590
1,700,000
1700
670
2,000,000
2000
788
2,500,000
2500
N/A
3,000,000
3000
N/A
Revised: May 19, 2016
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3.7.2 Natural Gas Piping
The table below should be used to size the natural gas piping to the appliance. The approximate
energy content of natural gas is 1,000 BTU / cu. Ft:
Pipe Capacity for Natural Gas
Nominal
Iron Pipe
Size
(Inches)
Internal Equivalent Pipe
Diameter Length
(Inches)
90o Ell
(Feet)
Maximum Capacity in Cubic Feet of Natural Gas Per Hour
Pressure Drop of 0.5” W.C.
Equivalent Length of Pipe (in feet)
Tee
(Feet)
20
40
60
80
100
150
200
1- 1/2
1.610
4.02
8.04
1460
990
810
2
2.067
5.17
10.3
2750
1900
1520
1300
1150
950
800
2- 1/2
2.469
6.16
12.3
4350
3000
2400
2050
1850
1500
1280
3
3.068
7.67
15.3
7700
5300
4300
3700
3250
2650
2280
4
4.026
10.1
20.2
15800
10900
8800
7500
6700
5500
4600
3.7.3 Propane Gas Piping
The table below should be used to size the propane gas piping to the appliance. The approximate
energy content of propane gas is 2,500 BTU / cu. Ft:
Pipe Capacity for Propane Gas
Nominal
Iron Pipe
Size
(Inches)
Internal Equivalent Pipe
Diameter Length
(Inches)
90o Ell
(Feet)
Maximum Capacity in MBH Propane Gas
Pressure Drop of 0.5” W.C.
Equivalent Length of Pipe (in feet)
Tee
(Feet)
10
20
40
80
150
300
1- 1/4
1.380
3.45
6.90
1900
1305
900
1- 1/2
1.610
4.02
8.04
2850
1960
1345
925
2
2.067
5.17
10.3
5490
3770
2590
1780
1270
870
2- 1/2
2.469
6.16
12.3
8740
6010
4130
2840
2020
1390
3.7.4 Pressure Testing the Gas Piping
The appliance and all gas piping connections should be pressure-tested and must be checked for leaks
before being placed into service. The appliance must be disconnected at the manual shut-off valve
(located at the end of the supplied gas train) from the gas supply piping during any pressure testing of
the system at pressures in excess of 0.0723 psig (2" W.C.). Perform the pressure test with
compressed air or inert gas if possible.
Some leak test methods, including the use of soap and water, may cause corrosion of the carbon steel
gas pipe fittings. If using soap and water or a similar leak test method, make sure to clean off all
moisture from the gas pipe fittings prior to placing the appliance into service.
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
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3.7.5 Sample Piping Diagram – MFD & VELOX Series Boilers
NOTE: Refer to Appendix D for best piping practices for both new and retrofit boiler
installations.
Revised: May 19, 2016
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3.7.6 Sample Piping Diagram – MFD & VELOX Series Water Heaters
NOTE: Refer to Appendix D for best piping practices for both new and retrofit water heater
installations.
Revised: May 19, 2016
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3.7.7 Water Piping Accessories & Connections (for Installer)
Strainer
To avoid possible contamination of the boiler or water heater with dirt, rust or sediment from the
system, a strainer near the boiler inlet is strongly recommended. Even new systems may contain
sufficient foreign material to eventually reduce the performance of the heat exchanger. Adequate
circulation of good clean water is essential for maximum efficiency and long life of the appliance. Refer
to Appendix D for more information on best piping practices in new and retrofit installations.
Relief Valve Piping
Each appliance is supplied with a pressure-relief valve sized in accordance with ASME requirements.
The relief valve discharge must be piped to an acceptable drain at a safe point of discharge. Reducing
couplings or other restrictions are not permitted in the discharge line.
Low Water Cut-off
The MFD and VELOX boilers and water heaters can accommodate an external low water cutoff device,
which may be required by the local jurisdiction. If the water level in the boiler drops below the probe,
the appliance will shut down and a LOCKOUT LOW WATER LEVEL will be displayed on the NURO
control. The low water cut-off will automatically reset when the low water condition clears; however the
NURO control will retain the lockout condition until the reset button on the display is pressed.
NOTICE! Some local jurisdictions may require an auxiliary low water cut-off device installed in
the external piping. The auxiliary low water cutoff device only prevents operation when the
water level in the appliance is insufficient. It does not detect low water conditions in other parts
of the system. Installation of automatic air vents in the “high points” of the piping or additional
low water safety devices should be considered to protect the system.
Drain Valve and Piping
The MFD and VELOX boilers and water heaters feature a ¾” drain connection. Prior to draining the
appliance, electrical power and gas supply must be turned off to the appliance, and the appliance must
be isolated from the system at the supply and return connections.
NOTICE! The 3/4” manual drain is for draining the water inside the heat exchanger only, not
the entire hydronic or domestic system. Draining the entire system through the boiler or water
heater’s drain valve will deposit sediment and debris from the system inside the heat
exchanger. This will result in poor heat transfer and premature failure. Refer to Appendix D
for more information on best piping practices.
Combustion Chamber Drain Piping
The MFD & VELOX boilers and water heaters feature a ½” condensate drain pipe which allows any
condensate that forms in the combustion chamber to drain. Connect this drain pipe to a common
condensate drain system.
Piping with Refrigeration Systems
When installed in a two-pipe system that provides both chilled and hot water, the control system should
be configured so as to limit the time rate of change of temperature at the boiler. Consult your authorized
Harsco Industrial, Patterson-Kelley boiler representative for application guidance.
Piping with air handling units
The boiler piping system of a hot water heating boiler connected to heating coils located in air handling
units, where they may be exposed to refrigerated air circulation, must be equipped with flow control
valves or other automatic means to prevent gravity circulation of the boiler water during the cooling
cycle
Revised: May 19, 2016
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3.8 Water Quality
The MFD/VELOX heat exchanger consists of copper finned-tubes. The heat exchanger requires proper
water conditions to remain efficient and function properly. Information of proper water treatment can be
found on our website www.harscopk.com type in search: “water quality”. For information, please refer to
Harsco Industrial, Patterson-Kelley Multi-Metal Systems Water Quality Standards as it appears in
Appendix C as this applies to the warranty of your heat exchanger.
NOTICE! The chemical manufacturer for use must certify glycol or other treatment chemicals
added to the system in multi-metal systems that include a copper heat exchanger.
Under no circumstances should petroleum based cleaning or sealing compounds be used in
the boiler system.
Under no circumstances should the hydronic system be flushed while the appliance is
attached to the system since the debris or corrosion products may accumulate in the
appliance and obstruct the appliance’s heat exchanger.
If the piping system attached to this unit will be chemically cleaned, the appliance must be
disconnected from the system and a bypass installed so that the chemical cleaning solution does not
circulate through the appliance. Following chemical cleaning, the system should be thoroughly rinsed
to remove cleaning agents prior to reconnecting the appliance to the system.
3.9 Pre-Start Checklist
Never attempt to operate an
appliance that has failed to
pass all the safety checks
described below. Operating
an appliance that has failed a
safety check could result in
injury. Bypassing safety
mechanisms will result in
unsafe appliance operation
which could result in injury or
death.
After checking controls by
manual adjustment, make
sure they are always reset to
their proper settings.
NOTICE!
If the expected error code(s) do
not appear, call for qualified
service.
Revised: May 19, 2016
Release May 17, 2016
Before attempting to start the appliance, make sure the following items
have been completed.
 Inspect the gas train, blower, ignition electrode, and appliance in
general to be sure there was no damage during shipment or
installation.
 Flue gas from the appliance is properly vented.
 Gas connection has been made, pressure tested for leakage, and
the line purged of air. Make sure all required vents have been
installed.
 Water connections are complete and the appliance and system
have been filled and purged of air.
 The appliance is connected to the correct electrical power source
listed on the nameplate, a disconnect having adequate overload
protection is required.
 Combustion air openings are not obstructed in any way and have
adequate capacity.
 The appliance is placed the proper distance from any combustible
walls.
 Relief valves have been piped to an acceptable drain at a safe
point of discharge.
 Combustion chamber drain piping is properly connected.
 Verify system water quality is within specifications.
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3.10 Safety Checks
The following checks of safety systems must be made before putting
the appliance into normal operation. Before firing the appliance refer
to Section 4 for information on the use of the controls, lighting, and
shut-down procedures.
3.10.1 Ignition Safety System Test
Test the ignition system safety shutdown as follows:
1. Cycle the appliance on by generating a heat request. (The
method for this will depend on the control setup.)
2. During the pre-purge cycle (before ignition), smoothly close
the downstream manual isolation valve (inside the
appliance’s cabinet) to restrict the gas flow.
3. Closing the manual isolation valve will prevent a successful
ignition, and the NURO control will display either:
109: “Ignition Failed”
110: “Ignition Failure Occurred”
The user should become
thoroughly familiar with the
operation of the appliance and
controls before attempting to
make any adjustments.
Changing parameters requires
an understanding of the
parameters and the
functionality of the appliance.
The appliance may not function
properly if parameters are
changed from the factory
values.
These alarms indicate an ignition failure and the lockout will remain until the NURO control is manually
reset via the on-screen prompts. After completing this test, turn the appliance off, open the
downstream manual isolation valve, then turn the appliance back on.
3.10.2 Manual Reset High Temperature Limit Test
The appliance is furnished with a manual reset high temperature limit which features a probe installed
near the appliance’s outlet (supply) in order to measure the outgoing supply water temperature. This
probe is connected to the manual reset high temperature limit by a thin, metal capillary tube. The
manual reset high temperature limit is located inside the appliance’s front door, toward the top of the
control panel and is identified with a yellow label.
Test the manual reset high temperature limit control as follows:
1. Cycle the appliance on by generating a heat request. (The method for this will depend on the
control setup.)
2. Allow the appliance to proceed through ignition until main flame is established.
3. Using a flathead screwdriver, turn down the setting on the manual reset high temperature limit
to its lowest value. Turning the screwdriver counter-clockwise decreases the temperature
setting.
4. When the outgoing supply water temperature exceeds the setting on the manual reset high
temperature limit, the main burner will shut off.
The NURO touchscreen will display 10009: “High Temperature Limit”. Return the system to normal
operation by readjusting the setting on the manual reset high temperature limit to its desired setting,
press the reset button on the manual reset high temperature limit, and finally touch any prompts from
the NURO control.
Revised: May 19, 2016
Release May 17, 2016
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3.10.3 Low Gas Pressure Switch Test
The appliance is furnished with a low gas pressure switch, installed near the appliance’s main gas
shutoff/control valve and is factory-set to 2” W.C. The operation of this switch must be checked as
follows:
1. Cycle the appliance on by generating a heat request. (The method for this will depend on the
control setup.)
2. Allow the appliance to proceed through ignition until main flame is established.
3. Manually increase the setting on the low gas pressure switch until the gas pressure is below this
newly adjusted value.
4. If gas pressure is too high to open the switch, reduce gas pressure below 5” W.C.
5. When the gas pressure drops below the newly adjusted value, the main burner will shut off.
When the low gas pressure switch opens, the NURO control will display 10012: “Low Gas Limit”.
This error will remain until the gas pressure is above pressure setting and the appliance is manually
reset.
NOTICE! After a successful test of the low gas pressure switch, make sure to readjust the
setting on the switch to 2” W.C.
3.10.4 High Gas Pressure Switch Test
The appliance is furnished with a high gas pressure switch, installed near the appliance’s main gas
shutoff/control valve and is factory-set between 2” W.C. and 3” W.C. The operation of this switch must
be checked as follows:
1. Before starting the appliance, close the downstream gas cock.
2. Cycle the appliance on by generating a heat request. (The method for this will depend on the
control setup.)
3. Allow the appliance to proceed to ignition.
4. When the gas pressure exceeds the setting of the high gas pressure switch, the main burner will
shut off.
When the high gas pressure switch opens, the NURO control will display 10011: “High Gas Limit”.
Even after re-opening the downstream gas cock, 10011: “High Gas Limit” will remain on the NURO
display until the appliance is manually reset.
3.10.5 Low Water Cut-out Test (If Applicable)
Some local jurisdictions may require an auxiliary low water cutoff device to be installed in the piping
external to the appliance. The probe is typically installed in the outlet (supply) piping, downstream of
the appliance.
NOTICE! If the auxiliary low water cutoff probe is to be installed in a horizontal pipe, make
sure the probe is installed in either the 3 o’clock or 9 o’clock positions (parallel to the floor) in
order to avoid nuisance errors.
In order to test the auxiliary low water cutoff device, press and hold the “TEST” switch for at least 5
seconds. A manual lockout reset error displaying 10010: “Low Water Limit” on the NURO touch
screen should occur. The auxiliary low water cutoff device may also have an LED indicator which will
change states during the test condition.
Revised: May 19, 2016
Release May 17, 2016
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All Rights Reserved.
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3.11 Burner Adjustment
3.11.1 Inlet Gas Test Port
NOTICE! Adjustments shall only be performed by a service representative specifically trained
and certified to perform maintenance on the Harsco Industrial, Patterson-Kelley equipment.
Verify proper operation after servicing.
Refer to the appliance’s rating plate for the minimum and maximum inlet gas pressures. The gas
pressure during main burner operation must be greater than the minimum indicated on the rating plate.
Nominal gas supply pressure 7” W.C. for natural gas and 11” W.C. for propane gas. The gas pressure
must not exceed 14” W.C. which is the maximum allowable pressure on the gas train components.
Each appliance is furnished with a manual shut-off valve with an integrated test port. This port is
located on the upstream side of the valve body for measuring supply pressure and is sealed with a
threaded plug.
Inlet Gas Test Port
The air flow is pre-set at the factory prior to shipment. Gas flow is primarily dependent on the
combustion blower, not the upstream gas pressure. The air/gas ratio may need to be adjusted in order
to obtain proper combustion readings for specific local conditions. A combustion analyzer must be
used. The probe must be placed in the appliance exhaust vent immediately after the appliance.
Combustion should be adjusted in accordance with Table of Combustion Exhaust Settings.
NOTICE! For high altitude adjustments (greater than 2,000 feet above sea level), see
Appendix B at the end of this manual.
Revised: May 19, 2016
Release May 17, 2016
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3.11.2 Manual Control Mode for High and Low Fire Adjustment
To adjust/tune combustion, use the NURO’s “Manual Control Firing Rate” mode. To access this mode,
press the “Info” button in the lower left corner of the screen, and then press “Service” in the lower left.
Next, touch “Press to Activate Manual Control” which will open the “Manual Control Firing Rate” mode.
This test mode should be used when adjusting or tuning the gas safety shut off/control valve on the
MFD & VELOX series boilers and water heaters.
NOTE: Proper water flow should be established before performing any combustion adjustments
to ensure the appliance doesn’t short-cycle or overheat.
Once in “Manual Control Firing Rate” mode, a heat request is required. Once the appliance cycles on
and is running in “Manual Control Firing Rate”, use the UP and DOWN arrows or the slider to force the
appliance to operate at low fire, high fire, or anywhere in-between. To prevent the appliance from
cycling off prematurely during adjustment, ensure that any load devices (air handlers, control valves,
radiators, air handling units, etc.) are in operation and are able to shed/dump the heat created by the
appliance.
Recommended Combustion Settings for P-K MFD Boilers and Water Heaters
Nominal
High Fire Setting
Low Fire Setting
Fuel
Inlet Gas
Pressure
% O2
% CO2
% O2
% CO2
Natural Gas
7" W.C
5.5 – 6.2
8.4 – 8.8
6.2 – 8.0
7.3 – 8.1
Propane
11" W.C
5.5 – 5.9
9.9 – 10.1
6.5 – 7.9
8.5 – 9.0
Recommended Combustion Settings for P-K VELOX Boilers and Water Heaters
Nominal
High Fire Setting
Low Fire Setting
Fuel
Inlet Gas
Pressure
% O2
% CO2
% O2
% CO2
Natural Gas
7" W.C
6.9 – 7.4
7.5 – 8.0
8.0 – 8.5
7.2 – 8.9
Propane
11" W.C
6.9 – 7.1
9.0 – 9.2
7.0 – 7.4
8.8 – 9.0
The MFD & VELOX boilers and water heaters are equipped with a combination gas/air control and gas
safety shut off control valve. The “zero governor” gas valve responds to the variable speed combustion
blower in order to supply the correct air/gas ratio for optimum performance and efficiency.
NOTICE! For high altitude adjustments (greater than 2,000 feet above sea level), see
Appendix B at the end of this manual.
Revised: May 19, 2016
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3.11.3 Adjusting High Fire Combustion
NOTE: ALWAYS adjust high fire combustion first!
Start the appliance and observe proper operating parameters for the
system. Access the “Manual Control Firing Rate”, as described above,
and increase the firing rate to 100%. Check combustion readings using
the combustion analyzer. If the combustion readings are not in
accordance with Section 3.11.2, adjust as follows:
Required Tools: Slotted screw driver/no 2.5 allen wrench, Combustion
analyzer and water tube manometer.
1. Using a slotted screw driver, set the maximum restrictor (high fire
screw) on the outlet/shutter flange of the combination gas safety
shut off / control valve by turning clockwise or counterclockwise to
achieve the desired CO2 or O2 level. To increase the O2 level,
adjust towards the “-“ symbol to decrease gas flow. To decrease
the O2 level, adjust towards the “+” symbol to increase gas flow.
2. There will be a slight time delay between the adjustment and the
response of the CO2/O2 measuring instrument. Clockwise rotation
decreases gas flow. Counterclockwise rotation increases gas flow.
3.11.4 Adjusting Low Fire
Start the appliance and observe proper operating parameters for the
system. Access the “Manual Control Firing Rate”, as described above,
and decrease the firing rate to 1%. Once the appliance has reached low
fire operation, check combustion readings using the combustion analyzer.
If the combustion readings are not in accordance with Section 3.11.2,
adjust as follows:
1. Using a 2 mm hex wrench, adjust the pressure regulator offset
adjustment (pictured above) to achieve the desired CO2 /O2 level.
To increase the O2 level, adjust towards the “-“ symbol to decrease
gas flow. To decrease the O2 level, adjust towards the “+”
Offset adjustment
symbol to increase gas flow.
2. Adjustments to the offset pressure regulator should not exceed ¼
turn at a time before allowing the readings to respond and stabilize.
Following all gas valve adjustments, check for proper light-off and verify correct fuel/air mix and
combustion quality throughout the entire firing range (from low fire to high fire).
3.11.5 Checking Flame Signal
Press the “Info” button on the NURO touch screen to load the “Information Screen” and scroll down to
view the flame signal measured in Volts. Typical flame signals should read between 20-50V. If the
flame signal is below 10V, the UV scanner may need to be replaced.
Revised: May 19, 2016
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3.12 Initial NURO Control Setup & Adjustment
This manual covers basic NURO control setup and adjustment. For a walkthrough of the complete
control setup, please refer to the NURO Boiler Controller: Advanced User’s Guide, Part Number is
1004905979 which is helpful for more complex installations. For more complex boiler or water heater
applications and more information on the parameters, please refer to the NURO Advanced User’s
Guide.
3.12.1 Startup
When the boiler or water heater is powered on, the NURO touchscreen will display an initial Startup
Screen then the Local Representative screen. This shows the name, address and phone number of
the local HARSCO Industrial representative.
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3.12.2 Home Screen
After a brief time, the Local Representative information screen will timeout displaying the Home
Screen. The Home Screen shows a snapshot of the boiler or water heater’s current operating
conditions:




Outlet (Supply) Temperature
Inlet (Return) Temperature
Exhaust Temperature
Firing Rate, etc.
Pressing the “Info” button in the lower left corner will load the Information screen.
For the setup wizard, press the “Settings” button in the lower right corner to load the “Settings” or
“Main Menu” screen.
3.12.3 Information Screen
The Information Screen contains real-time read-only values such as temperatures, relay states, etc.
Scroll through the Information Screen by sliding your finger up or down.
This screen is helpful to determine the operating characteristics of the boiler or water heater.
NOTE: For more information on any parameter, please refer to the NURO Boiler Controller:
Advanced User’s Guide; Part Number is 1004905979.
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3.12.4 Setup Wizard
The Setup Wizard is recommended for all boilers and water heaters
because it guides the user through setup for multiple applications
(Standalone Comfort Heat, Standalone Domestic How Water, and/or
Cascade operation). The Setup Wizard will guide the user through the
parameter setup for all the relevant applications based on responses
to a series of questions. To access the Setup Wizard, press <SETUP
WIZARD> from the “SETTINGS” menu [Figure 3.8.1].
While navigating the Setup Wizard, press the desired buttons in the
center content area. The selected choice will be indicated with a
yellow light as seen below. To proceed to the next Setup Wizard
screen, press <NEXT> at the bottom of the screen. The NURO®
control also allows the user to back-track at any time by pressing
<PREVIOUS> in the bottom-left corner of the screen.
The Setup Wizard allows the user to assign functionality to the userconfigurable Relays A through D. This allows the user to assign
functions like “Boiler Pump”, “System Pump”, “Flame Detected”, and
“Air Damper” to the relays.
NOTE: The relay assignments must agree with the wiring to/from the appliance. For example,
if Relay A is user-configured to enable/disable the Boiler Pump, the control wires to operate the
boiler pump must be properly wired to the Relay A terminals in the High Voltage (TB2) terminal
block.
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4 Operations
4.1 NURO Touchscreen Control System
4.1.1 Power On/Off Switch
After the appliance has been installed in compliance with this manual,
it is necessary to access the power (on/off) switch located in the
upper-left corner under the hinged sheet metal cover as shown below:
Do not use this appliance if any
part has been under water.
Immediately call a qualified
service technician to inspect the
appliance and to replace any
part of the control system and
any gas control which has been
under water. Failure to do so
could result in electrocution,
injury, or death.
If overheating occurs or the gas
supply fails to shut off, do not
turn off or disconnect the
electrical supply to the pump.
Instead, shut off the gas supply
at a location external to the
appliance.
NOTICE!
The On/Off switch only interrupts
power to the NURO control. In
order to fully remove power to the
entire appliance, use the external
disconnect.
NOTE: The operating instructions can be found on either the left side of the
unit or on the backside of the hinged sheet metal cover
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4.1.2 NURO Touch Screen Interface and Control Panel
Once the power switch is in the “ON” position, the P-K appliance can be programmed and operated
with the NURO touch screen interface located on the front door as shown below. A clear plastic cover
protects the touch screen which can be opened by pinching the clasp and swinging open to the left.
The NURO touch screen interface features a patented design which allows the user to rotate the
control 90° for service clearance. After opening the appliance front door, pinch the upper and lower
spring plungers to free the control assembly from the frame. This feature allows for up to 90° of travel
so the user can access the electrical components behind the display.
NOTE: Always return the NURO control to the default position (facing out through the front
door) before closing the appliance’s front door. Failure to do so could result in damage to the
NURO control or wiring.
4.1.3 Factory Tests
Safe lighting and other performance criteria were met with the gas manifold and control assembly
provided on this boiler when the boiler underwent factory tests specified in ANSI Z21.13/CSA 4.9, latest
edition. The same applies to water heaters which underwent factory tests specified in ANSI
Z21.10.3/CSA 4.3, latest edition. (See "Factory Firetest" label on the rear surface of the appliance).
Revised: May 19, 2016
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4.2 Normal Lighting and Shut-down Procedures
4.2.1 Normal Lighting Procedures
1. Make sure the system is filled with water and water is circulating in the system. Turn on
electrical supply and open the gas supply valves to the appliance.
2. Turn the on/off switch to the “On” position. If an error is indicated, refer to the NURO Advanced
User’s Guide to troubleshoot the problem and take necessary corrective action before
proceeding.
3. Set the desired high temperature limit and operating temperature. The NURO controller will now
begin the automatic firing sequence.
4.2.2 Normal Shut Down Procedures
1. Allow the appliance to turn off on its own once the temperature satisfies, or remove the call for
heat to the appliance.
2. Once the appliance completes a successful “Post-Purge” and “Post-Pump”, it will return to
“Standby”.
3. Once in standby, turn the on/off switch to the “Off” position.
4. Close all manual gas valves on the gas train.
5. Turn off the electrical disconnect to the appliance.
4.3 Emergency Shut-Off
In case of emergency, immediately shut off gas at the
rear of the appliance.
Manual gas
shutoff valve
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5 Maintenance
Lockout/tagout procedure
must be employed when
servicing this unit. Failure to
do so could result in
electrocution, injury, or death.
Label all wires prior to
disconnection when servicing
controls. Wiring errors can
cause improper and dangerous
operation.
Use care when reassembling
the main gas line and ensure
all connections are tight. Use a
leak detector to check for leaks
before and after servicing any
component of the gas piping.
Failure to do so could result in
injury or death.
Use care when servicing the
appliance to prevent the
accumulation of gas in or
around the combustion
chamber. Pockets of
accumulated gas are subject to
combustion and/or explosion
which could result in injury or
death.
Determine the cause of any
lockout or errors before
resetting the appliance. If able
to determine cause of lockout,
take appropriate corrective
action. If unable to determine
cause of the problem, call a
qualified service technician.
Verify proper operation after
servicing.
5.1 Preventative Maintenance
NOTICE! Proper maintenance schedule and record keeping is
critical for optimum performance and to maintain the Harsco
Industrial, Patterson-Kelley warranty.
NOTE: The combustion blower motor is permanently lubricated
and does not require periodic lubrication.
5.1.1 Daily Preventative Maintenance
Observe operating temperature and general conditions. Make sure
that the flow of combustion and intake air to the appliance is not
obstructed. Determine the cause of any service codes or lockouts
on the display panel. Observe any unusual noises or operating
conditions and make the necessary corrections. Notify responsible
individuals for required corrective action or repair.
Check daily to be sure that the
immediate area around the boiler or
water heater is free and clear of any
combustible materials, including
flammable vapors and liquids.
5.1.2 Weekly Preventative Maintenance
Observe the conditions of the main flame. A normal high fire flame
is mostly orange with a blue halo. A normal low fire flame will glow
reddish-orange. However, do not attempt to adjust the flame “by
eye”.
Correct air adjustment is essential to the efficient operation of this
appliance. Ensure that the flow of combustion and ventilation air is
not obstructed. If an adjustment in the combustion appears
necessary, the flue gas composition should be checked with a
carbon dioxide (CO2) or oxygen (O2 ) analyzer and compared to the
values stated in the Combustion Setup and Adjustment combustion
settings table (Section 3.11.2) If an adjustment to the combustion is
necessary, call a qualified and knowledgeable installer or service
agency that has been trained on the Harsco Industrial, PattersonKelley appliance.
Check daily to be sure that the
appliance area is free and clear
of any combustible materials,
including flammable vapors
and liquids.
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5.1.3 Monthly Preventative Maintenance
1. Press the “Info” button on the NURO touch screen to load the Information Screen and scroll
down to view the flame signal measured in Volts. Typical flame signals should read between 2050V. If the flame signal is below 10V, the UV scanner may need to be replaced.
2. Test the low water level cut-off. Refer to Section 3.9.2 Low Water Cut-out Test (if applicable).
3. Test the manual reset high-temp limit. Refer to Section 3.10.3 Manual Reset High Temperature
Limit Test.
4. Test the low gas pressure switch. Refer to Section 3.10.4 Gas Pressure Switch Tests.
5. Test operating temperature controls by reducing or increasing temperature settings as
necessary to check burner operation.
6. Check the combustion chamber drain piping for leaks or obstructions.
NOTICE! Installation and service must be performed by a qualified installer or service agency
that has been trained on the appliance.
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5.2 Maintenance and Inspection Schedule
This schedule applies when the appliance is in constant use. The section is divided into critical semiannual and annual maintenance followed by scheduled routine maintenance.
NOTICE! Proper maintenance schedule and record keeping is critical for optimum performance
and to maintain the Harsco Industrial, Patterson-Kelley warranty.
5.2.1 Semi-Annually
In addition to the recommended monthly service:
1. Clean burner of any accumulated dust or lint. Refer to Section 5.3.
2. Inspect burner for any signs of deterioration or corrosion. Replace immediately if deterioration or
corrosion is evident.
3. Check the water quality of the system fluid in accordance with Appendix C.
4. Inspect and clean the combustion chamber drain piping and check for leaks or obstruction.
5. Check the gap between the electrode and ground rod. For Natural Gas, the gap should be 1/8”
(+1/16”, -0”). For Propane Gas, the gap should be exactly 1/8”.
5.2.2 Annually
In addition to the recommended monthly and semi-annual service:
1. Inspect and clean the inlet screen of any accumulated dust.
2. Check burner and clean off any soot or foreign material that may have accumulated. Check for
corrosion of the burner and its parts. If there is evidence of deterioration or corrosion, replace
immediately. Inspect the combustion chamber when the burner is removed for inspection. Note
any signs of deterioration. Refer to Section 5.3 for cleaning instructions if needed.
3. Inspect and clean the copper finned tube heat exchanger. Clean the combustion side by
flushing with clean water and blowing dry with compressed air. Do not use any cleaning agents
or solvents. Do not use soap. A soft nylon brush may be used in accessible areas. Be sure to
inspect the condensate collection pan that is the lowest part of the heat exchanger.
4. Replace the ignition electrode and gasket.
5. Check the gap between the electrode and ground rod. For Natural Gas, the gap should be 1/8”
(+1/16”, -0”). For Propane Gas, the gap should be exactly 1/8”.
6. Drain and flush the water side of the heat exchanger as required (separate from system flush)
using clean water only.
7. Take a sample of system fluid and verify the water quality is in compliance as defined in
Appendix C.
8. Inspect the combustion chamber drain piping and check for leaks or obstruction.
9. Examine the venting system. Refer to the vent manufacturer's instructions for requirements in
addition to those listed below.
a. Check all joints and pipe connections for tightness.
b. Check pipe for corrosion or deterioration. If any piping needs replacing, do so
immediately.
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c. Inspect and clean any screens in the vent terminal.
10. Qualified service personnel should thoroughly inspect the heating system and correct any
problems prior to re-starting the appliance.
11. Perform combustion analysis ankd readjust as necessary according to the Combustion Setup
and Adjustment combustion settings table. Refer to Section 3.11
12. Perform a leak test of the gas valves in accordance with the manufacturer's instructions.
5.3 Cleaning the Burner & Combustion Chamber
Harsco Industrial, Patterson-Kelley recommends cleaning the burner and combustion chamber at least
once annually. A list of the required replacement (consumable) parts and tools are provided below:
Required Replacement Parts
Appliance Size
Part
Burner Gaskets
Ignition Assembly
Gasket
Ignition Electrode
Ground Rod
750 - 1000
Burner Gaskets
Ignition Assembly
Gasket
Ignition Electrode
Ground Rod
1500 – 1700 – 2000
Burner Gaskets
Ignition Assembly
Gasket
Ignition Electrode
Ground Rod
2500 – 3000
Part Number
23-0000-0327
23-0000-0354
23-0000-0077
23-0000-0484
23-0000-0485
23-1300-0033
23-1300-0035
23-0000-0077
23-0000-0282
23-0000-0127
23-0000-0382
23-0000-0462
23-0000-0437
23-0000-0466
23-0000-0467
Tools Required
Screwdrivers
Wrenches / Sockets

Flat Head

Pipe Wrench

Phillips Head

7/16” Socket

1/2” Socket
Cleaning Supplies

Pressurized Fresh Water
Supply

Hose w/ Nozzle

SimpleGreen or similar
mild detergent
NOTE: Spare parts and replacement parts can be ordered from Harsco Industrial, PattersonKelley be calling toll free (877) 728-5351. Reach us by fax at (570) 476-7247.
(Step-by-step instructions on next page)
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1. Lockout/tagout gas supply to the boiler or water heater.
2. Lockout/tagout electrical power to the boiler or water heater.
3. Use a flat-head screwdriver to remove the top and side panels and open the front door of the
appliance.
4. Protect the electrical and control components from exposure to water with towels, a nylon tarp,
or plastic wrap.
5. Locate the blower and burner assembly bolted to the top of the copper finned-tube heat
exchanger. Refer to Section 6.2.1, Section 6.2.5, and Section 6.2.6 for an illustration of these
components.
6. Disconnect the two wire plug connectors from the blower motor.
7. Disconnect the clear and blue tubing from the air/gas mixer head. NOTE: These tubes are
color-coded and must be correctly reinstalled.
8. Follow the model-specific instructions below to remove the blower and air/gas mixer head
assembly:
(750 through 2000):

Use a pipe wrench to disconnect the gas pipe union inside the appliance’s cabinet.

Next, use a 1/2” socket to remove the four (4) nuts from the lower flange on the
blower.

Carefully lift the blower motor and air/gas mixer head assembly out the top of the
appliance and set aside in a safe place.

Carefully remove the blower gasket and set aside in a safe place.
(2500 through 3000):

Use a pipe wrench to disconnect the gas pipe union outside the appliance’s cabinet.

Remove the two screws from the cover plate directly above where the gas piping
enters the appliance’s cabinet and then remove the cover plate itself.

Next, use a 7/16” socket to remove the four (4) nuts, the lock washer and flat washer
from the lower flange on the blower.

Set these parts aside in a safe place for reuse.

Next, carefully lift the blower motor and air/gas mixer head assembly out the top of the
appliance and set aside in a safe place.

Carefully remove the blower gasket and set aside in a safe place.
9. Disconnect the UV scanner, ignition wire, ground wire and the high exhaust back pressure
switch wire plug.
10. Remove the Phillips head screws from the ignition assembly and carefully lift the ignition
assembly out of the combustion chamber and set aside in a safe place. Remove and discard
the ignition electrode and ground rod.
11. Remove the ignition assembly gasket and discard.
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12. Use a 1/2” socket to remove the four (4) nuts and flat washers from the burner mounting plate
and set these parts aside in a safe place. Follow the model-specific instructions below in order
to remove the burner cylinder:
(750 through 1000):

First, remove the burner hood and set aside in a safe place.

Next, remove and discard the upper burner gasket (23-0000-0354 w/ 5.5” I.D.).

Next, carefully lift the burner cylinder out of the appliance’s combustion chamber.
Take extra precaution to prevent damage to the burner’s mesh while removing from
the combustion chamber.

Finally, remove and discard the lower burner gasket (23-0000-0327 w/ 5.8” I.D.).
(1500 through 2000):

First, use a 7/16” socket to remove the four (4) nuts and set aside in a safe place.

Next, remove the top cover plate and set aside in a safe place.

Next, remove and discard the upper burner gasket (23-1300-0033 w/ 7.5” I.D.).

Carefully lift the burner cylinder out of the appliance’s combustion chamber. Take
extra precaution to prevent damage to the burner’s mesh while removing from the
combustion chamber.

Remove the circular burner spacer plate and set aside in a safe place.

Finally, remove and discard the lower burner gasket (23-1300-0035 w/ 8.27” I.D.).
(2500 through 3000):

First, remove the burner hood casting and set aside in a safe place.

Next, remove and discard the upper burner gasket (23-0000-0462 w/ 6.6” I.D.).

Next, carefully lift the burner cylinder out of the appliance’s combustion chamber.
Take extra precaution to prevent damage to the burner’s mesh while removing from
the combustion chamber.

Finally, remove and discard the lower burner gasket (23-0000-0382 w/ 5.72” I.D.).
After removing from the appliance, use pressurized water (approximately 40 psig) to thoroughly
rinse and clean the cylindrical burner.
NOTE: Do not attempt to wash the burner while installed in the appliance. When cleaning the
burner, use a mild detergent such as Simple Green® to help loosen built-up debris trapped in
the burner mesh.
13. Locate the ½” combustion chamber drain pipe on the rear contact surface of the appliance
(close to the floor). The drain pipe should be connected to a drain system; ensure this is free
from obstruction and can drain freely. If the ½” pipe cap is installed on the drain pipe notify the
installer to connect this appliance to an adequate drain.
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14. With the burner removed, the open burner hole provides access to the appliance’s combustion
chamber / heat exchanger. Use pressurized water (approximately 40 psig) to thoroughly rinse
and clean the inside of the appliance’s combustion chamber. When cleaning the combustion
chamber, use a mild detergent such as Simple Green to help loosen built-up debris trapped in
the copper finned-tubes.
Be very careful when cleaning to avoid spraying any of the electrical
or control components. Water may cause a short circuit and damage
circuitry.
15. After several minutes of washing, turn off the hose and allow all the wash water to drain out of
the combustion chamber.
16. Follow the model-specific instructions below to install new burner gaskets and reinstall the
burner cylinder:
(750 through 1000):

First, install a new lower burner gasket (23-0000-0327 w/ 5.8” I.D.) and make sure the
circular openings for the ignition assembly face the front surface of the appliance.

Next, carefully reinsert the burner cylinder into the combustion chamber and align the
ignition assembly holes with the lower gasket.

Finally, install a new upper burner gasket (23-0000-0354 w/ 5.5” I.D.) and make sure
to align the ignition assembly holes.
(1500 through 2000):

First, install a new lower burner gasket (23-1300-0035 w/ 8.27” I.D.) and make sure
the circular openings for the ignition assembly face the front surface of the appliance.

Next, reinstall the circular burner spacer plate before reinserting the burner cylinder
into the combustion chamber and aligning the ignition assembly holes with the lower
gasket.

Install a new upper burner gasket (23-1300-0033 w/ 7.5” I.D.) and make sure to align
the ignition assembly holes.

Finally, reinstall the top cover plate and use a 7/16” socket to tighten the four (4) nuts
and compress the gaskets to seal this assembly.
(2500 through 3000):

First, install a new lower burner gasket (23-0000-0382 w/ 5.72” I.D.) and make sure
the circular openings for the ignition assembly face the front surface of the appliance.

Next, carefully reinsert the burner cylinder into the combustion chamber and align the
ignition assembly holes with the lower gasket.

Finally, install a new upper burner gasket (23-0000-0462 w/ 6.6” I.D.) and make sure
to align the ignition assembly holes.
17. Reinstall the four flat washers and use a 1/2” socket to tighten the four (4) nuts on the edges of
the burner mounting plate.
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18. Install a new ignition assembly gasket:

(750 through 2000): 23-0000-0077

(2500 through 3000): 23-0000-0437
19. Install a new ground rod and ignition electrode and refer to Section 5.1.1 for proper spacing of
the spark gap:
 (750 through 1000): 23-0000-0484 Ignition Electrode & 23-0000-0485 Ground Rod

(1500 through 2000): 23-0000-0282 Ignition Electrode & 23-0000-0127 Ground Rod

(2500 through 3000): 23-0000-0466 Ignition Electrode & 23-0000-0467 Ground Rod
20. With a new ignition assembly gasket, ground rod and ignition electrode installed, reinsert the
ignition assembly into the hole. Tighten the two Phillips head screws to compress the gasket
and seal this assembly.
21. Carefully reinstall the blower gasket before reinstalling the blower and air/gas mixer head
assembly on top of the burner assembly per the model-specific instructions below:

(750 through 2000): Reinstall the four (4) 5/16-18 nuts on the blower’s flange. Use a pipe
wrench to retighten the gas pipe union inside the appliance’s cabinet.

(2500 through 3000): Align the black rubber grommet to the entrance area for the gas
piping and reinstall the cover plate and two (2) screws to secure the gas piping. Reinstall
the four (4) flat washers, lock washers and 1/4-20 nuts on the blower’s flange. Reconnect
the gas flange to the gas valve by reinstalling and tightening the four (4) screws.
22. Reconnect the two wire plug connectors to the blower motor.
23. Reconnect the UV scanner, ignition wire, ground wire and high exhaust back pressure switch
wire plug to the ignition assembly.
24. Reconnect the air/gas mixer sensing tubes.
NOTE: These tubes are color-coded and must be correctly reinstalled. The clear tubing must
be reconnected to port on the air “cage” and the blue tubing must be reconnected to the port
on the air/gas mixer cylinder.
25. Remove the temporary protection (towel, tarp or plastic wrap) from the electrical and control
components.
26. Reattach the top and side panels to the appliance.
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
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5.4 After Repairs or Maintenance
Following any major repairs or preventative maintenance, follow the steps below before returning the
appliance to service.
1. Follow “Section 3.9 Pre-Start Check List” and all safety checks in “Section 3.10 Safety
Checks”.
2. Check the gas pressure, refer to Section 3.11.1 Inlet Gas Port to ensure proper operation of the
appliance.
3. Perform combustion check (Refer to Section 3.11.3 and Section 3.11.4) and adjust air/gas
mixture at high fire & low fire if the O2% or CO2% are out of range.
NOTE: Installation and service must be performed by a qualified installer or service agency
that has been trained on the Harsco Industrial, Patterson-Kelley appliance!
5.5 Sequence of Operations
If any “Manual Reset” limit
device trips, DO NOT reset
without determining and
correcting the cause. Manual
Reset Limits include: Flame
safeguard, high or low gas
pressure, high temperature
limit, stack temperature, low
water level. Attempting to
operate an appliance without
diagnosing the cause of failure
can result in unsafe operation,
increasing the risk of injury.
Never attempt to bypass a
safety limit device.
NOTICE!
Once the appliance begins the
ignition sequence, the firing
sequence may continue until
main flame is reached regardless
of heat request. The sequence
can be interrupted by turning the
power switch off.
Revised: May 19, 2016
Release May 17, 2016
1. When the On/Off switch is turned on, power is provided through
over-current protection (fuse and/or circuit breaker) to the NURO
control and the combustion blower.
2. For boilers operating in Comfort Heat (CH) mode, when the outlet
(supply) water temperature drops below “CH SETPOINT” minus
“CH DIFFERENTIAL ON”, a heat request is generated.
3. For water heaters operating in Domestic Hot Water (DHW) mode,
when the outlet (supply) water temperature drops below “DHW
BOILER SETPOINT” minus “DHW BOILER DIFFERENTIAL
ON”, a heat request is generated.
4. Provided all interlocks are made and the remote enable signal (if
installed) is active, the appliance will attempt to start.
5. The NURO control checks to make sure the air pressure switch is
open indicating there is no airflow through the appliance. The
combustion blower is then driven towards the pre-start fan speed.
When the air pressure switch closes, the “PRE PURGE TIME”
timer is started. Once the “PRE PURGE TIME” timer expires, the
blower is driven to the ignition speed.
6. A trial for ignition begins and the sequence of events is illustrated
graphically on the next page. A valid flame signal must be
detected within 4 seconds after the gas valves open (total
elapsed time 7 seconds).
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
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7. After a successful ignition, the fan is driven to low fire and the “CH LOW FIRE HOLD TIME”
timer or “DHW LOW FIRE HOLD TIME” is started. Once the applicable “LOW FIRE HOLD
TIME” timer expires, the appliance is released to modulation.
8. The NURO control modulates the firing rate between low and high fire to maintain the desired
outlet water temperature.
9. For boilers operating in Comfort Heat (CH) mode, the burner will continue firing until the outlet
(supply) water temperature exceeds “CH SETPOINT” plus “CH DIFFERENTIAL OFF”. At this
temperature, the gas valves are closed and the combustion blower continues to run until the
“POST PURGE TIME” timer has expired.
10. For water heaters operating in Domestic Hot Water (DHW) mode, the burner will continue firing
until the outlet (supply) water temperature exceeds “DHW BOILER SETPOINT” plus “DHW
BOILER DIFFERENTIAL OFF”. At this temperature, the gas valves are closed and the
combustion blower continues to run until the “POST PURGE TIME” timer has expired.
11. When the outlet water temperature is reduced by the load on the system, a heat request is
generated. The operating sequence will resume at Step 4.
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
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5.6 Troubleshooting
The NURO control will display graphical and/or text based error descriptions to announce any problems
with the appliance. There are two types of lockouts: manual reset lockouts which require the operator
to physically press the on-screen or device’s reset button, and automatic reset lockouts which will selfreset when the error condition clears. For a comprehensive list of errors and potential resolutions, please
refer to the NURO Advanced User’s Guide.
Should the unit fail to operate, call a qualified service technician to troubleshoot the problem and
implement corrective actions.
5.6.1 Loss of Power
In the event of a power failure, the NURO touch screen will go dark and the entire appliance will deenergize. The signal relays used to command auxiliary devices connected to the appliance (air
dampers, pumps, etc.) will also lose power, so these devices will deactivate. When power is restored,
the sequence of operation will resume at Step 4 (Section 5.5). If any error/lockout errors were present
at the time of the power failure, the NURO control will retain that error/lockout when power is restored.
5.6.2 Loss of Water Flow
The paddle type flow switch opens when there is an insufficient water flow through the appliance. The
NURO control will display 272: “Flow Switch Not Closed”, close the gas valve, and lock the appliance
out. When the water flow is corrected and the on-screen reset button is pressed, the appliance will
reset and resume operation at Step 4 (Section 5.5).
5.6.3 Low Gas Pressure
The low gas pressure switch opens when there is (or has been) insufficient gas pressure available for
proper operation of the appliance. If an external gas-supply shut-off valve is closed for any reason, a
low gas condition will result. The NURO control will display 10012: “Low Gas Limit”, close the gas
valve, and lock the appliance out. When proper gas pressure is restored, and the on-screen reset
button is pressed, the appliance will reset and resume operation at Step 4 (Section 5.5).
5.6.4 High Gas Pressure
The high gas pressure switch opens when there is (or has been) excessive gas pressure for the proper
operation of the appliance. The NURO control will display 10011: “High Gas Limit”, close the gas
valve, and lock the appliance out. When proper gas pressure is restored and the on-screen reset
button is pressed, the appliance will reset and resume operation at Step 4 (Section 5.5).
5.6.5 High Water Temperature
When the outlet (supply) water temperature has exceeded both the operating temperature limit and the
manual reset high-temperature limit, the NURO control will display 10009: “High Temperature Limit”,
close the gas valve, and lock the appliance out. When the outlet (supply) water temperature falls below
the high-limit temperature setting, the appliance will remain locked out until the high-temperature limit
switch is manually reset and the on-screen reset button is pressed. Once reset, the control will resume
operation at Step 4 (Section 5.5).
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
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5.6.6 Low Air
If the NURO control displays either 65: “Interrupted Airflow Switch OFF” or 66: “Interrupted Airflow
Switch ON”, this indicates improper airflow through the appliance. First, verify proper standby blower
operation – when the appliance is in “Standby”, the blower should also be in standby.
Next, check for obstructions of the combustion air intake and/or exhaust (flue) piping. Next, check the
hoses leading to the air switches are not kinked or obstructed. An error related to the air switch does
not necessarily mean that the air switch is defective.
When 66: “Interrupted Airflow Switch ON” is displayed, check that the air switch is open when the
blower is offline. Ensure there is no air flow through the appliance when the blower is offline. An
excessive negative draft in the flue piping can cause air flow through the offline appliance which may be
strong enough to maintain closure of the air switch.
When 65: “Interrupted Airflow Switch OFF” is displayed, check that the air switch is closed when the
blower is running. If the air switch does not close within 5 minutes during purge, the appliance locks
out. Check that the burner is clean (Cleaning the Burner, Section 5.3) and that there are no
obstructions to airflow in the intake or exhaust ducts.
5.6.7 Flame Failure
In the event of a flame failure, the NURO control may display one of the following error messages:





106: “Flame Lost in Main Flame Establish Period”
107: “Flame Lost Early in Run”
108: “Flame Lost in Run”
109: “Ignition Failed”
110: “Ignition Failure Occurred”
When 109: “Ignition Failed” or 110: “Ignition Failure Occurred” is displayed, the appliance did not
light during the trial for ignition. Check that the ignition electrode, ignition wire, and gas valve are
functioning properly. Check that the direct spark ignition is visible through the flame observation port
during the trial for ignition.
When 106: “Flame Lost in Main Flame Establish Period”, 107: “Flame Lost Early in Run”, or 108:
“Flame Lost in Run” is displayed, the appliance lost the flame signal during operation. Check that
combustion is adjusted properly, the gas pressure is correct, and the ignition electrode, ignition wire,
and gas valve are functioning properly.
5.6.8 Flame Error
In the event of a flame error (premature or late flame signal), the NURO control will display 105:
“Flame Detected Out of Sequence”. This may be caused by a failed/leaking gas valve or a flame rod
malfunction. If gas valve leakage is suspected, the unit must be isolated by turning off the main gas
supply line. Lockout/tagout the appliance until qualified and knowledgeable service personnel are
available to evaluate and repair or replace the failed parts. Check that the incoming gas pressures
have not exceeded 14” W.C. (1/2 psig).
5.6.9 Flue Problem
When the normally-closed high exhaust back pressure switch opens, the NURO control will display
10013: “High Back Pressure Limit”. This may be caused by an obstruction in the flue piping, an
obstruction in the combustion air intake, or a blocked condensate system. When the blockage is
removed, the boiler will automatically restart. If no blockage is found, it may be necessary to replace
the high exhaust back pressure switch.
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
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6 Parts/Technical Support
Spare parts and replacement parts can be ordered from
Harsco Industrial, Patterson-Kelley by calling toll free (877)
728-5351. Reach us by fax at (570) 476-7247.
Refer to the parts list shown on the assembly drawings
provided in this manual.
Technical information is also available by calling or visit the
Harsco Industrial, Patterson-Kelley website:
www.harscopk.com.
When ordering replacement parts please have the model
number and serial number of your boiler or water heater
available.
Typical schematic drawings and information about the low
and high voltage terminals are shown on the following
pages. Drawings specific to your particular boiler or water
heater can also be supplied by your local Harsco Industrial,
Patterson-Kelley representative.
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
Use of Non-Factory Authorized
replacement parts are not
recommended for this equipment.
All control components are
engineered for safety and are
designed to work in unison with
each of the other components.
Use of non-factory authorized
replacement parts jeopardizes the
functionality of the safety
features as well as the
performance of the appliance.
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6.1 Terminal Block Assignments and Wiring Diagrams
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
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6.1.1 Terminal Block Assignments — High Voltage (TB2) Terminal Block
Terminal
Label
Number
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
Description
MASTER ALARM RELAY
MASTER ALARM RELAY
RELAY A
RELAY A
RELAY B
RELAY B
RELAY C
RELAY C
RELAY D
RELAY D
GROUND
[120V+] AIR DAMPER
AIR DAMPER INTERLOCK
[120V+] AUXILIARY INPUT
AUXILIARY INPUT
[120V+] LOW WATER
LOW WATER CUTOFF
START INTERLOCK #1
START INTERLOCK #1
START INTERLOCK #2
START INTERLOCK #2
GROUND
Normally-Open Dry Contact, Close on Alarm
(240VAC Max Voltage & 1/2Amp Max Current)
NEUTRAL
N for 208-240VAC, Single phase, 60Hz
HOT L2
HOT L1
L2 for 208-240VAC, Single phase, 60Hz
L1 for 208-240VAC, Single phase, 60Hz
Revised: May 19, 2016
Release May 17, 2016
User-Configurable Normally-Open Dry Contact A
(240VAC Max Voltage & 1/2Amp Max Current)
User-Configurable Normally-Open Dry Contact B
(240VAC Max Voltage & 1/2Amp Max Current)
User-Configurable Normally-Open Dry Contact C
(240VAC Max Voltage & 1/2Amp Max Current)
User-Configurable Normally-Open Dry Contact D
(240VAC Max Voltage & 1/2Amp Max Current)
Ground Terminals for I/O Devices
120VAC Pilot-Duty for Air Damper End Limit Switch
Contact Closure When Air Damper Proven Open
Reserved for Future Use
120VAC Pilot-Duty for Auxiliary/External Low Water
Cutoff Device
External Interlock Circuit #1
(110-120VAC, Single phase, 60Hz)
External Interlock Circuit #2 (In Series w/ #1)
(110-120VAC, Single phase, 60Hz)
G for 208-240VAC, Single phase, 60Hz
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
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6.1.2 Terminal Block Assignments — Low Voltage (TB1) Terminal Block
Terminal Label
Number
Description
27
ECOM 3
26
ECOM 2
25
ECOM 1
24
MODBUS SHIELD
23
MODBUS COM B
22
MODBUS COM A
21
MODBUS/CASCADE REF
20
CASCADE B TO B
19
CASCADE A TO A
18
CASCADE SHIELD
17
GROUND
16
ANALOG OUTPUT [-]
Wireless Outdoor Air Receiver
2-Wire MODBUS RS485 & Shield Terminal
Reference Terminal (Application Dependent)
2-Wire Cascade & Shield Terminal
Ground Terminal for I/O Devices
15
4-20mA Analog Output Tracks Boiler Firing Rate
4-20mA ANALOG OUTPUT [+] 100% Firing Rate = 20mA, 1% Firing Rate = 4mA
14
NIGHT SETBACK
13
NIGHT SETBACK
12
OUTDOOR TEMP SENSOR
11
OUTDOOR TEMP SENSOR
10
DHW STAT / SENSOR
9
DHW STAT / SENSOR
8
HDR TEMP SENSOR
7
HDR TEMP SENSOR
6
SPARE ANALOG INPUT
5
SPARE ANALOG INPUT
4
ANALOG INPUT [-]
3
4-20mA ANALOG INPUT [+]
2
ENABLE / DISABLE
1
ENABLE / DISABLE
Revised: May 19, 2016
Release May 17, 2016
Contact Closure Enables Night Setback Operation
Open Circuit Disables Night Setback Operation
Outdoor Air Temperature Sensor for ODA Reset
(12kΩ Sensor)
DHW Enable Circuit Configurable for SPST Breakon-rise Aquastat or 12kΩ Tank Sensor
Hydronic Supply Header Temperature Sensor
(12kΩ Sensor)
Reserved for Future Use
4-20mA Analog Input
Configurable for Setpoint or Firing Rate Control
Contact Closure Enables Comfort Heat Operation
Open Circuit Disables Comfort Heat Operation
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
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6.1.3 MFD/VELOX NURO Wiring Diagram
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
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6.2 Parts Identification
6.2.1 Main Assembly
1
2
3
Mark
1
2
3
4
5
6
7
8
Description
Removable Top Covers
Burner & Blower Assembly
Terminal Box
Gas Train
Sheet Metal Cabinet
Heat Exchanger
NURO Control Panel
Front Door Assembly (Hinged)
4
5
6
7
8
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
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6.2.2 NURO Control Panel
10
1
2
3
4
5
9
8
Mark
1
2
3
4
5
7
Description
Blower Motor Relay
Transformer XFMR3 (20VA)
NURO Touchscreen Assembly
Fuse Holder
SOLA Mainboard
Revised: May 19, 2016
Release May 17, 2016
6
Mark
6
7
8
9
10
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
Description
Air Pressure Switch
Transformer XFMR2 (40VA)
Manual Reset Hi Temp Limit
Circuit Breaker
On/Off Switch
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6.2.3 Heat Exchanger Assembly (Sizes 750 through 2000)
12
1
13
2
11
10
9
3
4
5
8
6
7
Mark
1
Mark
8
Description
Combustion Wrapper
9
Flue Gas Temperature Switch
3
4
Description
Water Flow Paddle Switch
Supply/Outlet Casting
(2-1/2” NPT-F)
Flue Outlet
Inlet/Return Temperature Sensor
10
11
5
Inlet/Return Pipe (2-1/2” NPT-M)
12
ASME Nameplate
Upper Head Casting
Thermowell for Manual Reset High
Temperature Limit
2
6
7
Condensate/Washout Drain Cap
(3/4” NPT)
Lower Head Casting
Revised: May 19, 2016
Release May 17, 2016
13
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
Outlet/Supply Temperature Sensor
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1
6.2.4 Heat Exchanger Assembly (Sizes 2500 & 3000)
14
13
2
12
3
11
4
10
5
6
9
7
8
Mark
1
2
3
4
5
6
7
Description
Water Flow Paddle Switch
Supply/Outlet Casting
(3” 150# Flange)
Inlet/Return (3” 150# Flange)
Inlet/Return Temperature Sensor
Flue Outlet
Manual Drain Valve (3/4” NPT)
Condensate/Washout Drain
(3/4” NPT)
Revised: May 19, 2016
Release May 17, 2016
Mark
8
Description
Lower Head Casting
9
Combustion Wrapper
10
11
12
13
Flue Gas Temperature Switch
ASME Nameplate
Upper Head Casting
Outlet/Supply Temperature Sensor
Thermowell for Manual Reset High
Temperature Limit
14
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
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6.2.5 Gas Train, Burner & Blower Assembly (Sizes 750 through 2000)
1
3
9
2
4
5
6
7
8
Mark
1
2
3
4
5
6
7
8
9
Revised: May 19, 2016
Release May 17, 2016
Description
Combustion Blower / Fan
Internal (Downstream) Gas Cock
(1” NPT-F)
High Gas Pressure Switch
Main Gas Shutoff/Control Valve
External (Upstream) Gas Cock
1-1/2” (1700-2000)
1-1/4” (750-1500)
Low Gas Pressure Switch
Stainless Steel Mesh Burner
Ignition Electrode
High Exhaust Back Pressure Switch
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
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6.2.6 Gas Train, Burner & Blower Assembly (Sizes 2500 & 3000)
1
2
9
3
4
8
5
6
Mark
1
7
2
3
4
5
6
7
8
9
Revised: May 19, 2016
Release May 17, 2016
Description
Combustion Blower / Fan
Internal (Downstream) Gas Cock
(1-1/2” NPT-F)
High Gas Pressure Switch
Main Gas Shutoff/Control Valve
External (Upstream) Gas Cock
(2” NPT-F)
Low Gas Pressure Switch
Stainless Steel Mesh Burner
Ignition Electrode
High Exhaust Back Pressure Switch
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
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7 MODU-FIRE FORCED DRAFT & VELOX LIMITED WARRANTY
Subject to the terms and conditions herein and the Terms and Conditions of Sale (as defined herein), Harsco Industrial
Patterson‐Kelley (“Seller”) warrants to the purchaser of the product (“Buyer”) that the heat exchanger and burner are free of
defects in material and workmanship, when operated in accordance with the conditions stated herein, for a period of five (5)
years commencing on the date of shipment or, if a start‐up report is furnished to Seller, on the start‐up date shown on the
report furnished to Seller (the “Warranty Period”), provided that startup is completed within six (6) months of shipment and the
start‐up report is furnished to Seller within thirty (30) days of startup (this “Specific Limited Warranty”). The Exclusions and
limitations of liability set forth in the Terms and Conditions of Sale (as defined herein) apply to this Specific Limited Warranty.
Capitalized terms used but not defined herein have the meanings ascribed to them under Seller’s terms and conditions of sale
for the product, which can be found at http://harscopk.com/warranty.php (the “Terms and Conditions of Sale”). This Specific
Limited Warranty is transferrable to the owner that utilizes the product(s) purchased hereunder for its intended use at the
original installation site (the “Original Owner”). This Specific Limited Warranty is non‐transferable to anyone who subsequently
receives or purchases products from the Original Owner. If the Original Owner did not purchase the product directly from
Seller, the Original Owner should contact the reseller from whom it purchased the product for a copy of the Terms and
Conditions of Sale attached to the Order Acknowledgement received by the original purchaser of the product from Seller.
I.
REMEDY
Seller’s obligations under this Specific Limited Warranty is limited to repairing or, if in Seller’s judgment it seems more
appropriate, to furnishing without charge (installation not included), FCA Seller’s factory (Incoterms 2010), a similar part to
replace any part which after examination shall, to Seller’s own satisfaction be determined to have been defective at the time it
was shipped. In the event that a replacement is provided by Seller, the defective item will become the property of Seller.
Transportation to Seller’s facility or other designated facility for repairs of any products or party alleged defective shall, in all
events, be at Buyer’s sole risk and cost. This warranty applies only if the original installer and Seller (Attention: Harsco
Industrial, Patterson‐Kelley, 155 Burson Street, East Stroudsburg, PA 18301) receive, within the Warranty Period, an
immediate written notice, providing a detailed description of all claimed defects, upon discovery of such defects together with
proof of purchase (invoice or Order Acknowledgment) and a copy of the start‐up report for the affected product. Seller may
seek reimbursement of any costs incurred by Seller where the product is found to be in good working order, or when it has
been determined that this Specific Limited Warranty does not apply as per the exclusions set forth below. The remedies
available to Buyer set forth herein are exclusive remedies, and all other remedies, statutory or otherwise, including but not
limited to the right of redhibition, are waived by Buyer. Buyer acknowledges that the exclusion of remedies is neither
unreasonable nor unconscionable. Buyer shall indemnify and hold Seller harmless against, any claim due to any injury or
death to any person or damage to any property resulting in whole or in part from any modification or alteration Buyer makes to
any product sold hereunder.
II. EXCLUSIONS
To the full extent permitted by law, Seller shall have no liability for and the Warranties do not cover:
(A) any product which has been altered or repaired by other than Seller's personnel;
(B) deterioration or failure of any product due to
(i) abrasion, corrosion, erosion or fouling,
(ii) misuse,
(iii) modification not authorized by Seller in writing or
(iv) improper installation, lack of or improper maintenance or operation;
(C) equipment not furnished by Seller by the owner, either mounted or unmounted, or when contracted for by a party or parties
other than Seller to be installed or handled;
(D) the suitability of any product for any particular application;
(E) the design or operation of owner’s plant or equipment or of any facility or system of which any product may be made a
part;
(F) any damage to the product due to abrasion, erosion, corrosion, deterioration, abnormal temperatures or the influence of
foreign matter or energy;
(G) the performance of any product under conditions varying materially from those under which such product is usually tested
under industry standards at the time of shipment;
(H) leakage or other malfunction caused by:
(i) defective installations in general and specifically, any installation which is made
(a) in violation of applicable state or local plumbing, housing or building codes or
(b) contrary to the written instructions furnished with the product,
Revised: May 19, 2016
Release May 17, 2016
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All Rights Reserved.
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(ii) adverse local conditions in general and, specifically, sediment or lime precipitation in the tubes, headers and/or
shells or corrosive elements in the water, heating medium or atmosphere, or
(iii) misuse in general and, specifically, operation and maintenance contrary to the written instructions furnished with
the unit, disconnection, alteration or addition of components or apparatus, not approved by Seller, operation with
heating media, fuels or settings other than those set forth on the rating plate or accidental or exterior damage;
(I) production of noise, odors, discoloration or rusty water;
(J) damage to surrounding area or property caused by leakage or malfunction;
(K) costs associated with the replacement and/or repair of the unit including: any freight, shipping or delivery charges, any
removal, installation or reinstallation charges, any material and/or permits required for installation, reinstallation or repair,
charges to return the boiler and/or components;
(L) INCIDENTAL, SPECIAL OR CONSEQUENTIAL DAMAGES, SUCH AS LOSS OF THE USE OF PRODUCTS, FACILITIES
OR PRODUCTION, INCONVENIENCE, LOSS OF TIME OR LABOR EXPENSE INVOLVED IN REPAIRING OR REPLACING
THE ALLEGED DEFECTIVE PRODUCT;
(M) any claim due to any injury or death to any person or damage to any property resulting in whole or in part from any
modification or alteration Buyer makes to any product sold hereunder; and
(N) Design defects where Seller has complied with Buyer’s design specifications.
III. PROOF OF PURCHASE
Proof of purchase (invoice or Order Acknowledgement) and a copy of the start-up report for the affected product must be
provided to Seller when requesting service under this Specific Limited Warranty.
IV. ORDER OF PRECEDENCE
The Standard Limited Warranty set forth in the Terms and Conditions of Sale, (b) this Specific Limited Warranty and (c) any
applicable Extended Limited Warranty exclusively govern and control Seller’s and Buyer’s respective rights and obligations
regarding the warranty of the product. In case of any inconsistency, conflict, or ambiguity between the Standard Limited
Warranty, this Specific Limited Warranty and any applicable Extended Limited Warranty (collectively, the “Warranty
Documents”), the documents shall govern in the following order: (w) any applicable Extended Limited Warranty; (x) this
Specific Limited Warranty; (y) the Standard Limited Warranty and (z) other provisions in the Terms and Conditions of Sale.
Information identified in one Warranty Document and not identified in another shall not be considered a conflict or
inconsistency. No sales representative, agent, or employee of Seller or any reseller in the chain of sale of the product is
authorized to make any modification, extension, or addition to this Specific Limited Warranty, unless agreed to in writing by
Seller.
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
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8 Fire-Test Report
Date:
Appliance Serial #
Model #
Installation: Name:
City:
State:
Zip:
Contact
Installer Name:
Phone:
Type of Installation:
Fuel:
Natural Gas
(Hotel, School, etc.)
Propane
Outdoor Temperature Sensor Connected
Yes:
No:
Field Fire-Test
High
Low
DATE:
Inlet Gas
_____ "w.c.
_____ "w.c.
Oxygen (O2)
_____ %
_____ %
Carbon Dioxide (CO2)
_____ %
_____ %
Carbon Monoxide (CO)
_____ ppm
_____ ppm
Nox
_____ ppm
_____ ppm
Gross Stack Temp.
_____ ° F
_____ ° F
Combustion Air Temp.
_____ ° F
_____ ° F
Stack Press.(exhaust)
_____ "w.c.
_____ "w.c.
Main Flame Signal
_____ Volts or uA
_____ Volts or uA
Efficiency
_____ %
_____ %
Comb. Air Pres. (intake)
_____ "w.c.
_____ "w.c.
Lockup/Static Gas pressure
Gas pressure drop @ ignition
_____
2. Water Inlet temperature:
_____ ° F
3. Water Outlet temperature:
_____ ° F
4. Flow through boiler:
_____ GPM
5. Operating Temperature Setpoint:
6. Approximate stack lengths:
____
_____ ° F (from internal OR external control)
Ft. Horizontal
7. Incoming Electrical Power
_____ Volts a.c.
8. Sytem Water pH level
_____
_____ Ft. Vertical
_____ Flue Pipe Diameter
Less than 1 volt between neutral and ground
9. Comments:
Performed by PK
Certified Agent:
Start Up Certification #
________________
(Print Name)
A copy must be returned within 30 days of startup to Harsco Industrial Patterson-Kelley
Harsco Industrial Patterson-Kelley • 155 Burson Street • E. Stroudsburg, PA 18301
P) 570-476-7261 F) 570-476-7247 pkboilers@harsco.com
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
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Appendix A – Maintenance Log
Date
Hi Fire /
Low Fire
Revised: May 19, 2016
Release May 17, 2016
O2
CO
CO2
Stack
Temp
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
pH
Action
By
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Appendix B –Altitude Derate Schedule
For installations over 2,000 ft. elevation, a derate schedule is applied. The appliance’s input rating must
be reduced by 4% per 1,000 ft. which is illustrated in the graph below:
Although the appliance’s capacity is reduced due to the lower air density, the combustion tuning should
follow the standard combustion guidelines of Section 3.11. Tune the combustion for the same O2 and
CO2 levels as discussed in Section 3.11.
Revised: May 19, 2016
Release May 17, 2016
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All Rights Reserved.
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Appendix C –Water Quality Standard for Hydronic Boilers in MultiMetal Systems
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
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Appendix D – Best Practices For New & Retrofit Systems
BEST PRACTICES FOR ALL BOILER INSTALLATIONS
1. Patterson-Kelley recommends and most installation codes require isolation valves on both the
boiler’s inlet (return) and outlet (supply) pipe runs. These are used to hydraulically isolate the
boiler from the hydronic system, which should be standard practice when flushing or adding
concentrated cleaning chemicals.
2. Patterson-Kelley recommends installing purge valves on the system side of the boiler’s isolation
valves. These valves should be used to purge the hydronic system of debris and sediment prior
to the initial startup of the boiler equipment. Since the purge valves are located on the system
side of the boiler’s isolation valves, the debris and sediment will not be routed in direct proximity
to the boiler’s heat exchanger.
3. Patterson-Kelley recommends installing a standard mesh strainer (maximum 20 mesh) on the
each boiler’s return (inlet) piping. This is intended to prevent large particles, foreign debris, etc.
from entering and obstructing flow or heat transfer through the boiler’s heat exchanger. Each
strainer should feature a manual blow-down valve in order to purge the debris from the strainer.
NOTE: This strainer is not intended to remove fine particulate matter from the boiler system
which will be discussed later in this appendix.
4. Patterson-Kelley recommends installing a water meter on the cold water fill piping. The intention
of this device is to periodically monitor the amount of fresh water introduced into the system
piping. It can also be used to establish a rough estimate of the total system volume during the
initial fill. In general, the annual amount of fresh water make-up should be less than 10% of the
total system volume. A water meter can also be useful to detect a leak in the hydronic system if
you notice an unexpected increase in the volume of fill water.
5. Oxygen (O2) elimination is critical to the longevity of any hydronic system. Patterson-Kelley
recommends installing an Air Separator (micro-bubbler style) that is capable of eliminating the
dissolved Oxygen levels introduced from the cold water fill. In general, air separators are most
effective when the boiler water is at highest temperature and lowest pressure.
6. Patterson-Kelley recommends installing an Automatic Air Vent on the Air Separator. In order for
the Air Separator to continually purge the system of dissolved Oxygen, an Automatic Air Vent is
preferred over a manual air vent.
7. The maximum flow rate requirements vary between Patterson-Kelley boiler models. Please
refer to Appendix E for a complete listing of the maximum flow rates per boiler model.
Exceeding the maximum flow rate of a boiler can cause erosion of the boiler’s heat exchanger or
piping materials and can damage the paddle type flow switch.
8. The minimum flow rate requirements vary between Patterson-Kelley boiler models. Please refer
to Appendix E for a complete listing of the minimum flow rates per boiler model. Flowing below
the minimum flow rates can lead to overheating of the boiler’s heat exchanger materials and the
formation of steam bubbles within the water passages.
9. Well in advance of the equipment startup, turn off all circulation pumps and close the isolation
valves on each boiler’s inlet (return) and outlet (supply) pipe runs. Connect a hose to the purge
Revised: May 19, 2016
Release May 17, 2016
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valves and run this hose to a nearby floor drain. Open each purge valve to flush out debris that
is present in the water. This process may take several attempts until the discharge water is
sufficiently clean. After successfully purging the system, make sure to open the boiler’s isolation
valves and turn on the circulation pumps.
10. Upon startup, Patterson-Kelley recommends collecting two water samples: one from the
hydronic system and another from the cold water fill. It is best practice to circulate the hydronic
system for at least one hour prior to collecting this initial water in order to acquire a
representative (blended) sample.
11. Within the first three months after startup, Patterson-Kelley recommends collecting a follow-up
water sample from the hydronic system. This should be compared to the initial startup sample
in order to determine any changes in pH, Alkalinity, conductivity, etc. that may adversely affect
the system performance.
12. Although the ongoing water treatment regimen will vary based on the supplier and application,
Patterson-Kelley recommends a minimum annual water sample rate. The results of the annual
water tests should be compared to past tests in order to determine any changes in pH,
Alkalinity, conductivity, etc. that may adversely affect the system performance. Refer to
Appendix C for the water quality standard.
BEST PRACTICES FOR RETROFIT BOILER INSTALLATIONS
1. The primary concern in retrofit installations into existing boiler systems is the presence of
suspended and dissolved solids. These are typically a result of deteriorating piping, fittings, or
legacy boiler’s heat exchangers. Patterson-Kelley recommends installing a side-stream filter
(maximum 10 micron) to remove this existing particulate, sediment, etc. There are many
different types of side-stream filters available, Patterson-Kelley recommends consulting your
local water treatment provider in order to determine the best method for your particular
application.
2. If the existing hydronic system contains a significant amount of suspended and dissolved Iron,
Patterson-Kelley recommends the use of a side-stream filter with built-in magnet. This magnet
helps attract and eliminate the Iron particulate.
3. Some water treatment additives/chemicals may cause leeching from the existing system piping.
As more contaminants leech from the walls of the piping into the system water, the pH and the
level of Total Dissolved Solids (TDS) may gradually climb to levels that will adversely affect the
system performance. A side-stream filter will accommodate the increased TDS, but you may
need to consult your local water treatment provider in order to combat the increased pH.
BEST PRACTICES FOR NEW BOILER INSTALLATIONS
1. The construction of the hydronic system piping involves many different operations that can
introduce contaminants (weld slag, solder, flux, pipe dope, cutting oils, metal shavings, etc.) It is
critical to properly flush the system well in advance of startup of the boiler equipment.
2. In order to locate loose pipe connections, leaks, etc. after the initial construction of the hydronic
system piping, the Mechanical Contractor may fill and drain the system several times. During
these initial fill-ups and drains, Patterson-Kelley recommends closing the boiler’s isolation valves
in order to separate them from the hydronic system. This will help limit the amount of dissolved
Oxygen and particulates that are brought in direct contact with the boiler’s heat exchanger.
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
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BEST PRACTICES FOR ALL WATER HEATER INSTALLATIONS
1. Patterson-Kelley recommends and most installation codes require isolation valves on both the
water heater’s inlet (return) and outlet (supply) pipe runs. These are used to hydraulically
isolate the water heater from the system, which should be standard practice when flushing.
2. Patterson-Kelley recommends installing purge valves on the system side of the water heater’s
isolation valves. These valves should be used to purge the domestic hot water system of debris
and sediment prior to the initial startup of the water heater equipment. Since the purge valves
are located on the system side of the water heater’s isolation valves, the debris and sediment
will not be routed in direct proximity to the water heater’s heat exchanger.
3. Patterson-Kelley recommends installing a standard mesh strainer (maximum 20 mesh) on each
water heater’s inlet (return) piping. This is intended to prevent large particles, foreign debris,
etc. from entering and obstructing flow or heat transfer through the water heater’s heat
exchanger. Each strainer should feature a manual blow-down valve in order to purge the debris
from the strainer. NOTE: This strainer is not intended to remove fine particulate matter from the
domestic water system.
4. Oxygen (O2) elimination is critical to the longevity of any domestic water system. PattersonKelley recommends installing Automatic Air Vents in the “high points” of the piping in order to
purge the system of dissolved Oxygen and air. Automatic Air Vents are preferred over manual
air vents in order to continually purge the domestic water system.
5. The maximum flow rate requirements vary between Patterson-Kelley water heater models.
Please refer to Appendix E for a complete listing of the maximum flow rates per water heater
model. Exceeding the maximum flow rate of a water heater can cause erosion of the heat
exchanger or piping materials and can damage the paddle type flow switch.
6. The minimum flow rate requirements vary between Patterson-Kelley water heater models.
Please refer to Appendix E for a complete listing of the minimum flow rates per water heater
model. Flowing below the minimum flow rates can lead to overheating of the heat exchanger
materials and the formation of steam bubbles within the water passages.
7. Well in advance of the equipment startup, turn off all circulation pumps and close the isolation
valves on each water heater’s inlet (return) and outlet (supply) pipe runs. Connect a hose to the
purge valves and run this hose to a nearby floor drain. Open each purge valve to flush out
debris that is present in the water. This process may take several attempts until the discharge
water is sufficiently clean. After successfully purging the system, make sure to open the water
heater’s isolation valves and turn on the circulation pumps.
8. Upon startup, Patterson-Kelley recommends collecting two water samples: one from the
domestic hot water system and another from the cold water fill. NOTE: Water softening may be
required if the water samples indicate high levels of hardness.
9. Patterson-Kelley recommends a minimum annual water sample rate to determine any changes
in pH, Alkalinity, conductivity, etc. that may adversely affect the system performance.
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
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Appendix E – Installation and Quick Reference
Fuel/Gas Supply

Refer to Section 3.7 for information on proper sizing of the gas supply piping. Undersized gas
piping with too much pressure drop will negatively impact the boiler’s performance.

Install a lock-up type gas regulator to supply an appropriate gas pressure as described below:
Natural Gas
Minimum Inlet Pressure = 3.5” W.C. to 4.0” W.C.
Maximum Inlet Pressure = 14.0” W.C.
Propane Gas
Minimum Inlet Pressure = 11.0” W.C.
Maximum Inlet Pressure = 14.0” W.C.
NOTE: Harsco Industrial, Patterson-Kelley recommends installing an individual lock-up type
gas regulator in the gas supply piping to each boiler. For installations where one master lockup type gas pressure regulator will service multiple boilers, Patterson-Kelley recommends
contacting the local regulator representative for application assistance specifying the
appropriate lock-up type regulator and gas pipe sizing.
Electrical/Power Supply

Carefully inspect the boiler’s nameplate labels which describe the power supply requirements.

Provide an appropriate power feed to the boiler with overcurrent protection as described below:
Appliance Size
750 - 1000
1500 - 2000
2500 - 3000

Power Supply Requirements
208-240VAC, single phase, 60Hz sized for 10 Amps.
208-240VAC, single phase, 60Hz sized for 15 Amps.
208-240VAC, single phase, 60Hz sized for 20 Amps.
Prior to startup, carefully check all electrical connections for tightness as connections can come
loose during shipping.
Exhaust Venting


The P-K MODU-FIRE Forced Draft boilers and water heaters are dual-certified as Category II &
Category IV appliances, capable of operating with slightly negative to slightly positive exhaust
pressure. It is critical to ensure the flue venting material is suitable for use with the appliance.
o
For Category II installations, ensure the flue venting system is designed to maintain a
slightly negative exhaust pressure between -0.01” W.C. and -0.05” W.C.
o
For Category IV installations, ensure the flue venting system is designed to maintain a
positive exhaust pressure which must be in the following ranges:

+0.01” W.C. and +1.5” W.C. (MFD Sizes 750 through 2000)

+0.01” W.C. and +1.0” W.C. (MFD Sizes 2500 through 3000)
The P-K VELOX boilers and water heaters are certified as Category I appliances, designed to
operate under a slight negative exhaust pressure. It is critical to ensure the flue venting material
is suitable for use with the appliance
o
For Category I installations, ensure the flue venting system is designed to maintain a
slightly negative exhaust pressure which does not exceed -0.05” W.C.
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
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Hydronics/Water Flow (MFD & VELOX 750 - 1000 Sizes)
MODU-FIRE Forced Draft Boilers & Water Heaters: Minimum & Maximum Flow Rates
Flow
Condition
Maximum Flow
Optimal Flow
Minimum Flow
Minimum Flow
Minimum Flow
Operation
High Fire
High Fire
High Fire
Ignition
Low Fire
N750-MFD
W750-MFD
(5:1)
120 GPM
65 GPM
60 GPM
60 GPM
60 GPM
N1000-MFD
W1000-MFD
(6:1)
150 GPM
85 GPM
80 GPM
80 GPM
80 GPM
Approx. ΔT
10 °F
20 °F
21 °F
10 °F
4 °F
Approx. ΔT
11 °F
20 °F
21 °F
10 °F
3 °F
VELOX Boilers & Water Heaters: Minimum & Maximum Flow Rates
Flow
Condition
Maximum Flow
Optimal Flow
Minimum Flow
Minimum Flow
Minimum Flow
Operation
High Fire
High Fire
High Fire
Ignition
Low Fire
Revised: May 19, 2016
Release May 17, 2016
N750-VX
W750-VX
(1.2:1)
120 GPM
65 GPM
60 GPM
60 GPM
60 GPM
Approx. ΔT
10 °F
20 °F
21 °F
19 °F
17 °F
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
N1000-VX
W1000-VX
(1.6:1)
150 GPM
85 GPM
80 GPM
80 GPM
80 GPM
Approx. ΔT
11 °F
20 °F
21 °F
17 °F
13 °F
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Appliance Connections (MFD & VELOX 750 - 1000 Sizes)
All connections should be in compliance with national, state, and local code requirements.
NOTICE!
This is a non-condensing gasfired appliance and the
incoming (return) water
temperature MUST be
maintained above 130°F.
Dropping below 130°F will
cause acidic condensate to
form within the appliance’s heat
exchanger and damage the
copper finned-tubes.
NOTICE!
NOTICE!
The appliance is furnished with a capped
3/4” drain pipe which is used to drain builtup condensation inside the appliance’s
combustion chamber. Connect this 3/4”
drain pipe to the common drain piping.
Revised: May 19, 2016
Release May 17, 2016
Most installation codes require a 3/4”
manual drain (ball) valve to be installed at
the lowest point on the heat exchanger.
Make sure the appliance is isolated from the
heating system before using the manual
drain valve.
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
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Hydronics/Water Flow (MFD & VELOX 1500 - 2000 Sizes)
MODU-FIRE Forced Draft Boilers & Water Heaters: Minimum & Maximum Flow Rates
Flow
Condition
Operation
Maximum Flow
Optimal Flow
Minimum Flow
Minimum Flow
Minimum Flow
High Fire
High Fire
High Fire
Ignition
Low Fire
N1500-MFD
W1500-MFD
(6:1)
150 GPM
130 GPM
90 GPM
90 GPM
90 GPM
N2000-MFD
W2000-MFD
(6:1)
180 GPM
170 GPM
120 GPM
120 GPM
120 GPM
Approx. ΔT
17 °F
20 °F
28 °F
14 °F
5 °F
Approx. ΔT
19 °F
20 °F
28 °F
14 °F
5 °F
VELOX Boilers & Water Heaters: Minimum & Maximum Flow Rates
Flow
Condition
Maximum Flow
Optimal Flow
Minimum Flow
Minimum Flow
Minimum Flow
Operation
High Fire
High Fire
High Fire
Ignition
Low Fire
Revised: May 19, 2016
Release May 17, 2016
N1500-VX
W1500-VX
(1.5:1)
150 GPM
130 GPM
90 GPM
90 GPM
90 GPM
Approx.
ΔT
17 °F
20 °F
28 °F
23 °F
19 °F
N1700-VX
W1700-VX
(1.6:1)
165 GPM
145 GPM
100 GPM
100 GPM
100 GPM
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
Approx.
ΔT
17 °F
20 °F
29 °F
23 °F
18 °F
N2000-VX
W2000-VX
(1.8:1)
180 GPM
170 GPM
120 GPM
120 GPM
120 GPM
Approx.
ΔT
19 °F
20 °F
28 °F
22 °F
18 °F
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Appliance Connections (MFD & VELOX 1500 - 2000 Sizes)
All connections should be in compliance with national, state, and local code requirements.
NOTICE!
This is a non-condensing gas-fired
appliance and the incoming (return)
water temperature MUST be
maintained above 130°F. Dropping
below 130°F will cause acidic
condensate to form within the
appliance’s heat exchanger and
damage the copper finned-tubes.
NOTICE!
NOTICE!
The appliance is furnished with a capped
3/4” drain pipe which is used to drain builtup condensation inside the appliance’s
combustion chamber. Connect this 3/4”
drain pipe to the common drain piping.
Revised: May 19, 2016
Release May 17, 2016
Most installation codes require a 3/4”
manual drain (ball) valve to be installed at
the lowest point on the heat exchanger.
Make sure the appliance is isolated from the
heating system before using the manual
drain valve.
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
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Hydronics/Water Flow (N2500-MFD & N3000-MFD)
The chart below represents the pressure drop (Ft of Head) versus the water flow rate (GPM) for the
MODU-FIRE Forced Draft boiler models N2500-MFD & N3000-MFD. This information is useful to help
size an appropriate circulation pump. Keep in mind this pressure drop represents the boiler only,
additional consideration is needed for any connecting piping, valves, strainers, couplings, flanges, etc.
MODU-FIRE Forced Draft Boilers & Water Heaters: Minimum & Maximum Flow Rates
Flow
Condition
Maximum Flow
Optimal Flow
Minimum Flow
Minimum Flow
Minimum Flow
Operation
High Fire
High Fire
High Fire
Ignition
Low Fire
Revised: May 19, 2016
Release May 17, 2016
N2500-MFD
(5:1)
Approx. ΔT
N3000-MFD
(6:1)
Approx. ΔT
270 GPM
220 GPM
165 GPM
165 GPM
165 GPM
16 °F
20 °F
27 °F
13 °F
5 °F
325 GPM
265 GPM
165 GPM
165 GPM
165 GPM
16 °F
20 °F
32 °F
16 °F
6°F
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
1004905935 P-K MFD & VELOX 750-3000
Installation and Owners Manual (Rev B May2016).doc
Page 96
P-K MFD/VELOX Gas Fired Appliance
Technical Service 1.877.728.5351
Appliance Connections (N2500-MFD & N3000-MFD)
All connections should be in compliance with national, state, and local code requirements.
NOTICE!
This is a non-condensing boiler and the
incoming (return) water temperature must
be maintained above 130°F. Dropping
below 130°F will cause acidic condensate
to form within the appliance’s heat
exchanger and damage the copper finned
tubes.
NOTICE!
NOTICE!
The appliance is furnished with a capped
3/4” drain pipe which is used to drain
built-up condensation inside the
appliance’s combustion chamber.
Connect this 3/4” drain pipe to the
common drain piping.
The appliance is furnished with a 3/4”
manual drain (ball) valve which allows the
user to completely drain the heat
exchanger. Make sure the appliance is
isolated from the heating system before
using the manual drain valve.
Revised: May 19, 2016
Release May 17, 2016
 HARSCO Industrial, Patterson Kelley 2016
All Rights Reserved.
1004905935 P-K MFD & VELOX 750-3000
Installation and Owners Manual (Rev B May2016).doc
Page 97
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