Domestic heating by oil: boiler systems

Domestic heating by oil: boiler systems
Energy Efficiency Best Practice in Housing
Domestic heating by oil: boiler systems
Guidance for installers and specifiers
Space heating flow
Hot water
Flow
Space heating return
AIR
Cold supply
Return
Diagram 5
Air
Flue
Return
Drain
Flow
Flow
Air
Return
Contents
2
1. Introduction to Best Practice
3
1.1
Boiler efficiency
3
1.2
Energy consumption and emissions
4
2. UK building regulations
5
2.1
England and Wales
5
2.1.1New buildings
5
2.1.2Existing buildings
6
2.2
Scotland
7
2.3
Northern Ireland
8
8. System selection
- practical issues
24
9. Installing central heating
systems
29
9.1
‘Competent person’ requirements
29
9.2
Installing the boiler
29
9.3
Controls
32
9.4
Oil storage and supply
33
9.5
Water treatment
33
3. Boiler types
9
3.1
Regular boilers
9
10. Commissioning and handover
34
3.2
Combination boilers
9
10.1 Commissioning
34
34
3.3
Cooker boilers
10
10.2 Advising householders
3.4
Condensing boilers
10
10.3 Servicing
34
4. Systems and components
11
4.1
Sealed and 0pen-vented systems
11
Appendix A Exception procedure flowchart
35
4.2
Domestic hot water
11
4.3
Upgrading systems
12
4.4
Flue types
12
4.5
Heat emitters
14
Appendix B Notes to CHeSS 2005
36
4.6
Circulator pumps
14
Appendix C Definitions of boiler types
38
Appendix D Definitions of heating controls
39
References
41
5. Controls
15
5.1
Individual controls
15
5.2
Selecting controls
17
5.3
Further control improvements
18
6. Central Heating System
Specifications (CHeSS)
19
7. Energy Efficiency
21
7.1
Comparing boiler efficiencies
21
7.2
The Standard Assessment Procedure (SAP)
21
7.3
Energy consumption and running costs
22
7.4
Carbon dioxide emissions
22
7.5
The Boiler Efficiency Database
22
7.6
Saving energy with better controls
23
Section 1 - Introduction to Best Practice
Home energy use is responsible for 28 per cent of UK carbon emissions
which contribute to climate change. By following Best Practice standards,
new build and refurbished housing will be more energy efficient and will
reduce these emissions, saving energy, money and the environment
This guide is designed to help installers, specifiers and purchasers of
domestic central heating systems to select the most appropriate system for
their needs. It gives advice on how to achieve better energy efficiency,
lower running costs and reduced carbon dioxide (CO2) emissions.
In particular, this publication is concerned with the encouragement of Best
Practice.While the requirements for satisfying building regulations in
various parts of the UK are described, the main purpose is to explain how
to achieve considerably better performance through careful choice of
systems and practices.
This publication focuses on ‘wet’ or ‘hydronic’ central heating systems in
which the water is circulated to heat emitters from an oil-fired boiler.The
oil used would normally be kerosene although gas-oil is sometimes used for
domestic heating. Specifically, this publication addresses issues concerning
the selection of boilers, hot water storage vessels, controls and indeed
complete systems. It brings together information on most types of boiler
currently available, the systems to which they can be fitted and key points
to consider when choosing equipment for a particular installation. More
detailed information on the specification, installation and use of oil-fired
equipment is available from the Oil Firing Technical Association (OFTEC)
website at www.oftec.org.
1.1 Boiler efficiency
The efficiency of the boiler is the main factor in the overall efficiency of a
domestic central heating system.This is why minimum standards of
efficiency are required by law for most boiler types - as set out in the
Boiler Efficiency Directive and equivalent UK legislation (17,20). Best Practice,
though, requires substantially better performance.
The efficiency of the overall system in turn has a major impact on running
costs and the associated CO2 emissions. Boiler efficiency depends upon:
fuel;
boiler type and design;
the load on the boiler due to the weather;
boiler and radiator sizing relative to the design heat load;
system controls;
flow and return temperatures;
installation and commissioning;
regular servicing and maintenance.
•
•
•
•
•
•
•
•
When older boilers are replaced, the advances in boiler technology mean
that substantial efficiency improvements can be expected from newer
equipment. Manufacturers now design for maximum efficiency consistent
with durability.The greatest energy efficiency benefits are obtained from
installing condensing boilers - these are always more efficient than noncondensing models. In England and Wales it is a requirement of the building
regulations from 1 April 2007 that newly installed oil-fired boilers should be
condensing, with a Seasonal Efficiency of a Domestic Boiler in the UK
(SEDBUK) efficiency of 86 per cent or more, unless an exception is allowed
(see Section 2.1.2).
How to use this guide
The guide is set out as follows:
Section 2 explains the building regulations for heating and hot water
systems in different parts of the UK.
Sections 3, 4 and 5 go into some detail about the range of systems,
boilers and controls currently available.
Section 6 reproduces the Central Heating Systems Specifications
(CHeSS).These set out specifications for meeting the basic efficiency
levels needed to comply with building regulations as well as higher
performance levels regarded as current Best Practice.They can be used
as ready-made purchase specifications.
Section 7 focuses on the benefits to be obtained from choosing Best
Practice.
Why are condensing boilers more efficient?
A condensing boiler has a large heat exchanger which extracts more
heat from the flue gases. In a non-condensing boiler, the flue gases are
at a temperature of 120-200°C. In a condensing boiler, more heat is
removed and the temperature falls to below 100°C and as low as 50°C
for the most efficient boilers operating at reduced boiler return
temperature.The water vapour in the gases condenses (hence the
name) and the resulting liquid has to be drained away. As the heat
exchanger gets wet in the process, it is more susceptible to corrosion.
To avoid this, it has to be constructed from corrosion-resistant
materials eg. stainless steel.
For more information on different boiler types see Section 3.
Section 8 covers the practical issues affecting the selection of boilers,
systems and controls.
Section 9 is concerned with proper installation, especially with regard
to the flues and drains needed for condensing boilers, as well as oil
storage and supply issues.
Section 10 offers guidance on commissioning and other related issues
such as servicing and information to be provided to customers.
The appendices provide additional notes to the CHeSS specification,
together with definitions of different boiler types and controls.
Note: the superscript numbers in brackets in the text refer to
documents listed at the end of this guide.
3
Section 1 - Introduction to Best Practice
1.2 Energy consumption and
emissions
Boilers for heating and hot water represent the greatest proportion of
domestic CO2 emissions.They consume far more energy than household
appliances. For similar output, emissions are higher from oil-fired boilers
than from gas or LPG ones, even though oil boilers are normally more
efficient.
The average household with central heating consumes about 23,000
kilowatt-hours (kWh) of energy each year. Of this, nearly 84 per cent is for
heating and hot water.To reduce fuel costs and cut emissions, it is
particularly important to choose efficient boilers and install them in suitably
designed and controlled systems.
Figure 1: Heating and hot water as a proportion of
total energy usage in homes heated by oil
Energy
consumption
Other
16%
Boiler
84%
CO2 emissions
Other
23%
Boiler
77%
Relative costs
Other
45%
Boiler
55%
4
Section 2 - UK building regulations
This section outlines the minimum standards for heating efficiency as set
out in the building regulations.The remainder of this guide then
concentrates on Best Practice - a higher standard.
There are different building regulations in England and Wales, Scotland, and
Northern Ireland. All contain provisions for conservation of fuel and power
(22,23,24).These restrict the type of heating system that may be installed in
new dwellings. In the case of England and Wales, new and replacement
heating systems in existing dwellings are also covered. A summary of the
main points of the regulations is given below.
Other parts of the regulations (Part J in England and Wales, Section 3:
Environment in Scotland and Part L in Northern Ireland) deal with the
related issues of the safety of heating installations and with fuel storage.
U-values measure the rate of heat transfer through materials, in units
of watts per square metre per degree of temperature difference
(W/m2K).The lower the figure, the lower the rate of heat loss.
The Standard Assessment Procedure (SAP) is the UK Government’s
procedure for calculating home energy ratings, enabling the
householder to compare the energy performance of different buildings
(26). In SAP 2001 the index is a number from 1 to 120, where higher
numbers indicate greater efficiency. All new homes in the UK are
required to have a SAP rating to comply with the building regulations.
SAP 2001 is expected to be replaced by SAP 2005 in England,Wales
and Northern Ireland in January 2006.
The elemental method
Here, the boiler should have a SEDBUK efficiency at or above a ‘reference
efficiency’ of 85 per cent for regular oil-fired boilers or 82 per cent for oilfired combination boilers (combis).
The ‘target U-value’ method
The carbon index is calculated as part of SAP 2001. CO2 is emitted as a
result of burning fuel, or generating electricity, to meet the demand for
space and water heating. Expressed on a scale from 0.1-10.0, higher
values represent lower emissions.
In SAP 2005 the carbon index will be replaced by a Dwelling Carbon
Emissions Rate (DCER).
Under this method, an average U-value (see panel) is calculated from the
values for the various elements of the building envelope.This figure must
not exceed a target value for the structure. If the SEDBUK value for the
chosen boiler is different from the reference value referred to above, the
target U-value is adjusted to take account. In this case, the target U-value is
multiplied by the factor.
efficiency of proposed boiler (%)
reference value (%)
2.1 England and Wales
The building regulations set a legal requirement to make ‘reasonable
provision . . . for the conservation of fuel and power in dwellings’. However,
the approved guidance notes that ‘there may well be alternative ways of
achieving compliance’ (Part L1) and different strategies can be adopted
provided it can be shown they are at least as good as those given in the
guidance. More detailed guidance on this is available from the Office of the
Deputy Prime Minister (ODPM) website (21).
2.1.1 New buildings
New dwellings must comply with Part L1 of the regulations (22).Three
methods of demonstrating compliance are given using boiler efficiencies,
based on Seasonal Efficiency of Domestic Boilers in the UK (SEDBUK)
values. Only SEDBUK efficiency ratings are acceptable and the Boiler
Efficiency Database is the best source of this information (see
www.boilers.org.uk).
If the chosen boiler is less efficient than the reference value, the effect will
be to reduce the target U-value, requiring improved thermal performance
from the building fabric. If the boiler is more efficient, then more flexibility
in fabric insulation levels is permitted.
The carbon index method
The third method is the carbon index method (see panel) - a value of 8.0
or better must be achieved.The choice of fuel will have a direct impact on
the carbon index.
Storage vessels
Hot water storage vessels should be insulated in accordance with BS1566,
BS3198 or BS7206 (27,28,29), and the internal heat exchanger should be sized
accordingly.There should be pumped circulation through the primary circuit
to the heat exchanger. If a thermal store is used, it should meet the
requirements of the Waterheater Manufacturers’ Association 1999
performance specification (30).
5
Section 2 - UK building regulations
Controls
Zone controls should allow different air temperatures to be set for living
and sleeping areas (other than in small open-plan flats and other properties
where these areas are not separated). In most dwellings, both temperature
zones can be controlled by a single time switch or programmer channel.
However, in properties with a floor area of more than 150m2, multiple
timing zones are required (with no zone larger than 150m2).
Separate timing controls should be provided for hot water, unless this is
provided by a combi boiler.
Boiler interlock (see Section 5.1) is needed to ensure that the boiler is
switched off when neither heat nor hot water is wanted.Thermostatic
radiator valves (TRVs) alone will not provide a boiler interlock.These must
be supplemented by a room thermostat or other device to prevent
unnecessary boiler cycling.
Pipework
Pipes should be insulated wherever they pass outside the heated living
space. In addition, all hot water pipes connected to the hot water cylinder
(including the vent pipe and the primary flow and return) should be
insulated for at least 1m from the connection.
Commissioning
Upon completion of the installation, the system should be inspected and
then brought into service so that it operates efficiently and meets its
specified performance levels.The owner or occupier should also be given
information on the operation and maintenance of the system.The installer
(competent person) should provide details of the installation to OFTEC
who will send a certificate to the householder and supply any relevant
information to the local authority Building Control Department.
Alternatively installers or their customers can use the Local Authority
Building Control route for building regulation notification for which a
charge is made.
2.1.2 Existing buildings
Part L1 of the Building Regulations applies to work on ‘controlled services
or fittings’ in existing dwellings, as well as in new ones. Certain types of
heating system are ‘controlled’, including central heating systems with
boilers. Alterations to controlled services or fittings require a Building
Control Notice, unless they are carried out by a recognised competent
person allowed to self-certify the work.
In particular, any new boiler (whether or not it replaces an existing unit)
should meet or exceed the same reference efficiency as that quoted for a new
building, except in dwellings where the total floor area is less than 50m2.
From 1 April 2005 the reference efficiency is set at 86 per cent for existing
buildings - a level only achievable by condensing boilers.Where the
installation of a condensing boiler would be impractical or excessively
costly, it is reasonable to install a non-condensing boiler instead (see panel).
It has been agreed that all oil boilers installed before 1 April 2007 will
qualify automatically as a reasonable exception, and the minimum allowable
efficiency meanwhile remains at 85 per cent for regular oil-fired boilers or
82 per cent for oil-fired combis. Nevertheless, the assessment form from
6
the Condensing Boiler Installation Assessment Procedure should still be
completed when non-condensing boilers are installed in existing dwellings
in the period April 2005 to March 2007.
New or replacement hot water storage vessels and controls should meet
the same requirements as in new buildings. Ensuring adequate controls are
in place should be a priority whenever a boiler or hot water storage vessel
is installed. Commission and handover procedures should also be
undertaken as in new buildings.
Condensing boiler exceptions
To determine the conditions under which a non-condensing boiler is
accepted as reasonable, an assessment of the property should be
carried out following the Condensing Boiler Installation Assessment
Procedure.The procedure is shown in outline in Appendix A, and given
in full detail in (21).There is an assessment form, with instructions for
completion, and a technical guide.
Key points include the following.
The assessment considers fuel type, dwelling type, boiler position,
flue options, flue terminal positions and condensate drain points.
The lowest cost installation position must be found, as defined by
the procedure.
Standardised costs and benefits are assumed, which will not be the
same as actual costs and benefits in any particular property.
The installation position is based on the characteristics of the
empty building, ignoring furniture and fittings as well as any position
preferred by the owner.
A simple points system determines whether the lowest cost
installation option exceeds a fixed threshold.
The assessment form must be completed and signed by a
competent person and a copy given to the building owner, who
should retain it as evidence an assessment has been carried out.
A non-condensing boiler may then be installed.The form may be
needed when the building is sold.
Even if an exception is allowed, a condensing boiler is preferable
and a grant may be available to the householder to assist with the
extra installation cost.
The boiler installed, whether condensing or non-condensing, does
not have to be installed in the position evaluated for the purpose
of the assessment.
•
•
•
•
•
•
•
•
Section 2 - UK building regulations
elemental method (explained above), but if the boiler efficiency is lower
then the target U-value is multiplied by the following factor.
proposed boiler SEDBUK (%)
reference boiler SEDBUK (%)
The factor will have the effect of making the target U-value lower (i.e.
harder to meet).
The carbon index method
The third method of demonstrating compliance is the carbon index method
(see panel), by which a result of 8.0 or higher must be obtained when the
overall energy performance of the building is assessed under SAP. The fuel
used for heating and hot water directly affects the carbon index.
Storage vessels, pipework and controls
Hot water storage vessels must be adequately insulated, and all pipes used
for space heating and hot water supply must be suitably insulated where
they lie outside the heated living space.
The space heating system must be controlled by room thermostats or
TRVs, and an adjustable seven day time switch or programmer. Boiler
interlock (see Section 5.1) must ensure the boiler is switched off when
there is no requirement for heat or hot water.TRVs alone are not sufficient
to achieve boiler interlock, and must be supplemented by a room
thermostat or other device to prevent unnecessary boiler cycling.
2.2 Scotland
From 1 May 2005, new dwellings must comply with the Building (Scotland)
Regulations (23).There are three alternative methods of demonstrating
compliance in which the efficiency of the boiler is taken into account. In
each case the efficiency measurement to be used is SEDBUK (see Section
7.1), and the Boiler Efficiency Database (see Section 7.5) is the best source
of SEDBUK figures for all domestic boilers in the UK. Efficiency figures
other than SEDBUK are inadmissible.
Commissioning
At completion of installation, systems must be inspected, tested, and
brought into service so as to meet the specified performance and operate
efficiently.Written information on the operation and maintenance of the
system must be provided for the occupier.
The elemental method
The first method, known as the elemental method, distinguishes between a
boiler which has a SEDBUK efficiency above or below a ‘reference
efficiency’.The ‘reference efficiency’ is 85 per cent for oil-fired regular
boilers or 82 per cent for oil-fired combi boilers. If the boiler has a
SEDBUK efficiency below the reference efficiency, then lower (more
onerous) maximum U-values (see panel) are applied to the elements of the
building fabric, which will tend to increase construction costs.
The ‘target U-value’ method
The second method is known as the target U-value method, in which an
average U-value is calculated for the various elements of the building
envelope and must not exceed a target which depends on the ratios of
total floor, ground floor, and roof areas to the total area of all exposed
elements of the dwelling. No adjustment is needed to the target U-value if
the boiler meets or exceeds the reference efficiency level needed for the
7
Section 2 - UK building regulations
The elemental method
Under the elemental method, boiler efficiency is not specified explicitly,
although it affects the SAP rating achieved. If the SAP rating is 60 or less
then lower (more onerous) maximum U-values (see panel) are applied to
the elements of the building fabric.This will tend to increase construction
costs.
The ‘target U-value’ method
Under the target U-value method, the target is calculated by reference to
the total floor area and total area of exposed elements, and raised (i.e.
relaxed) where the SAP rating exceeds 60.The target can be relaxed further
by as much as 10 per cent where there is a high efficiency heating system.
A heating system with a gas boiler of seasonal efficiency above 72 per cent
qualifies, and between 72 per cent and 85 per cent, the target U-value may
be increased by up to 10 per cent pro rata. Above 85 per cent boiler
efficiency the target U-value may be increased by the maximum of 10 per
cent.
Storage vessels, pipework and controls
Hot water storage vessels shall be insulated to a specified standard, and all
hot water pipes connected to the vessel (including the vent pipe and
primary flow and return) shall be insulated for at least 1m from the
connection. Other pipes shall be insulated where they lie outside the
heated living space.
2.3 Northern Ireland
The relevant building regulations are the Building Regulations (Northern
Ireland) 2000, and specifically Building Regulations F3 and F4.These call for
‘reasonable provisions’ to be made for space heating and hot water supply.
The installation, alteration or replacement of any heating system must
comply with the relevant regulations. All new heating systems should be
notified to Building Control and any alteration to an existing heating system
where a structural alteration is also involved.Where an existing heating
system is extended, the extension to the system must be insulated to
comply with regulation F4.
‘Technical Booklet F: Conservation of fuel and power’ (24) gives provisions
that are deemed-to-satisfy the requirements of Regulations F3 and F4.
Although it is not essential to follow Technical Booklet F, it is obligatory to
comply with Building Regulations F3 and F4.
Technical Booklet F has two methods of demonstrating compliance,
explained here. For both methods a SAP rating (see Section 7.2) must first
be calculated, and different requirements then apply according to whether
or not the SAP rating exceeds 60.
8
The heating and hot water systems shall be controlled by thermostats or
TRVs, allowing for independent zones where different temperatures are
required (eg. separate sleeping and living areas). A time switch or
programmer shall be provided to control operating periods. Boiler interlock
(see Section 5.1) shall ensure the boiler is switched off when there is no
requirement for heat or hot water, and TRVs alone are not sufficient.They
shall be supplemented by other devices to prevent unnecessary boiler
cycling.
Section 3 - Boiler types
While this guide describes all types of oil-fired boilers, it concentrates on
condensing units which provide optimum performance with low running
costs and reduced CO2 emissions.
Modern oil boilers are very efficient with reasonably low running costs. As
such they are particularly suitable in areas where no mains natural gas is
available. LPG is also an option in this situation. See the gas boiler systems
guide for more information.
When seeking estimates of installation costs for oil-fired boilers, ensure
that the provision and installation of an adequate oil storage tank is taken
into account as well.
In most households, a single boiler provides both space heating and hot
water, either:
•
•
indirectly, through a regular boiler and separate hot water tank (which is
usually a copper cylinder with a heating coil inside); or
directly, using a combination boiler with no separate tank.
3.1 Regular boilers
3.2 Combination boilers
Combination or combi boilers provide both space and hot water heating
directly. Most oil-fired units are ‘storage combis’ and have an internal hot
water store.
These boilers are capable of providing a continuous flow of hot water, but
at a lower rate than typical hot water storage systems. As such, they may
be less suitable for dwellings where there may be simultaneous demands
for hot water ie multiple bathrooms.
Combi boilers save space because:
they are fed directly from the water main, with no need for a hot water
storage cylinder or cold water feed cistern;
they are usually intended for use in a sealed system which does not
require a feed-and-expansion cistern (allows a ‘dry’ roof space).
•
•
Before selecting a combi boiler, check the manufacturers’ instructions to
ensure that the dwelling has both satisfactory water pressure and an
adequately-sized water supply pipe. Otherwise, hot water service may not
be adequate.
Units that are not combination boilers (see below) are commonly referred
to as ‘regular’, ‘conventional’ or ‘heat only’ boilers.They can be wallmounted or floor-standing. Space heating is provided directly, but for hot
water they need to be connected to a separate hot water storage system.
Figure 3: Combi boiler
Space heating flow
Oil-fired back boilers with a ‘fuel effect’ fire on the front (usually electric
powered) can be installed in a fireplace, but condensing versions are not
available.
Hot water
Regular boilers for sealed systems (see Section 4.1) which have components
such as pumps and expansion vessels within their casings are known as
‘system boilers’.
Space heating return
Figure 2: Regular boiler
Cold supply
Space heating
Flow
The power (rate of heat output) of combi boilers is usually governed by
hot water service requirements, and often exceeds that needed for space
heating. Most oil-fired combis have fixed rate burners and a hot water
store.
Hot water
AIR
Return
A back boiler unit (BBU) is one designed to be installed within a fireplace.
Condensing BBUs are not available.
Factors to consider are:
the time taken for hot water to reach an acceptable temperature;
hot water flow rate at the acceptable temperature;
how long this rate can be sustained;
can hot water be drawn off at more than one point simultaneously?
•
•
•
•
9
Section 3 - Boiler types
These factors will be influenced by the following.
The size of the internal hot water store. A store can reduce the delay in
delivering hot water.There are four different types:
- instantaneous: no internal hot water store (rarely oil-fired);
- ‘keep hot’:
small or no internal hot water store - keeps
water within the boiler permanently hot to
reduce warm-up time at boiler start-up
(sometimes called ‘warm-start’);
- medium store: sufficient to meet small hot water requirements
without delay, but insufficient for a bath;
- large store:
sufficient for a bath or multiple simultaneous
draw-off without delay.
•
•
•
Power. Boiler power affects the rate at which hot water at the required
temperature can be drawn off after any internal store is exhausted.
Flow rate. Boilers generally limit the hot water flow rate to ensure the
declared temperature rise.
•
•
•
Room-sealed and open-flue models are available for domestic
applications.
Many have extended flue options.
Suitable for replacing most existing boilers (but not BBUs in the same
position).
Installation considerations for condensing boilers
•
•
•
•
•
They are as easy to install as non-condensing boilers, but need a
connection from the condensate outlet to a drain.
Can be installed in modern fully-pumped systems.
Oversized radiators will increase efficiency but good efficiency can still
be obtained with ‘normally sized’ radiators.
Care is needed in siting the flue terminal due to the plume of water
vapour usually present during boiler operation.The plume will be visible
for much of the time the boiler is in operation.
Can employ a range of extended flue options, with the visible plume less
likely to be a nuisance at high levels.
3.3 Cooker boilers
Some oil-fired cookers have a hot water boiler (either integral or separate).
The latest units have two burners: one is for heating and hot water; the
other is for cooking and has independent control.The casings of these
cooker boilers have relatively high heat loss, which can be useful in winter
but not in summer. Condensing units are not available.
3.4 Condensing boilers
Figure 4: Condensing boiler
Return
Drain
Condensing boilers are the only type that meet Best Practice requirements
and should always be considered as first choice in any application. In
England and Wales it is a requirement of the building regulations from 1
April 2005 that newly installed oil-fired boilers have a boiler exception form
completed. From 1 April 2007 boilers installed must be condensing, with a
SEDBUK efficiency of 86 per cent or more, unless an exception is allowed
(see Section 2.1.2). Even if an exception is allowed, a condensing boiler
should always be the first choice and a grant may be available to the
householder to assist with the extra installation cost.
Domestic oil-fired condensing boilers are usually only available for use with
kerosene. Refer to the boiler manufacturer when the use of gas-oil is being
considered.
Features of condensing boilers
•
•
•
•
•
10
SEDBUK efficiencies between 86 per cent and 97 per cent (with
kerosene as the fuel).
Typically a new condensing oil boiler will have an efficiency of 93 per
cent, compared with 85 per cent for a new non-condensing boiler and
60-70 per cent for older types.
The system does not need to be designed to make the boiler condense
all the time to achieve improved efficiency.
Mostly regular types but combis being introduced.
Mostly floor standing.
Flow
Section 4 - Systems and components
Systems may either be sealed to prevent ingress or escape of air, or openvented. In the past, most installations were open-vented, but many are being
replaced by sealed systems.Whether a system is sealed or open vented
makes no difference to its energy efficiency.
expansion cistern to allow for changes in water volume with temperature.
This cistern has to be at the highest point of the system, usually in the loft
space where it must be protected against freezing.
Figure 6: Open system
4.1 Sealed and open-vented
systems
Feed and expansion cistern
Sealed
This is a popular option for new systems and increasingly used for boiler
replacements.The feed-and-expansion cistern is replaced by an expansion
vessel incorporating a diaphragm to accommodate variations in water
volume. As the system is not open to the atmosphere, the pressure rises
with increasing temperature, and additional safety controls must be installed
(these are often within the boiler).The system will need a relief valve
connected to an external discharge point, which must be placed where any
discharge of hot water will be harmless.There is no permanent connection
to a water supply, and the system may have to be topped up with water
occasionally.
Figure 5: Sealed system
Expansion
vessel
4.2 Domestic hot water
The main issues to be considered regarding domestic hot water are:
the number of people in the dwelling;
the number of baths/showers/taps;
the hot water flow rate required;
likelihood of simultaneous hot water draw-offs;
availability of space for a hot water cylinder, or storage-combi;
importance of a dry loft;
feasibility of solar water heating.
•
•
•
•
•
•
•
Specific issues relating to combis are given in Section 3.2.
As the system is not open to the atmosphere, there is little possibility of
oxygen being absorbed into the water and, consequently, reduced risk of
corrosion. Because these systems may remove the need to install pipes and
cisterns in the roof space, they reduce the risk of freezing.
Most combi boilers and all system boilers are designed for use with sealed
systems and will usually incorporate system components, including a pump,
expansion vessel and safety controls within the boiler case. In such cases, it
must be ensured that this integral expansion vessel has sufficient capacity to
allow for the water expansion of the whole system.
Open-vented
The majority of existing systems with a regular boiler and an indirect hot
water cylinder are open vented. ‘Open vent’ refers to the separate vent
pipe which is open to the atmosphere.The system also needs a feed-and
Most existing regular boiler systems employ a vented, indirect, hot water
storage cylinder. In households with a single bathroom, these are typically of
117-140 litre capacity, but for larger dwellings with more than one bathroom
(and perhaps with separate shower facilities), a larger cylinder capacity will
be required (19). A larger cylinder will also be required, with an additional
heat exchanger, if a solar collector or other supplementary heat source is
to be exploited. A solar collector system, installed separately from the main
heating system but connected to a different heat exchanger in the same
cylinder, can make a significant contribution to hot water requirements, and
save boiler fuel. Separate guidance and advice on solar systems should be
sought (50). Alternative supplementary heat sources that may be connected
are a heat pump, or wood burning stove.
High performance cylinders contain a rapid heating coil.This is a heat
exchanger with larger surface than normal, which reduces the time taken to
heat the water and may reduce boiler cycling. It gives a valuable reduction
in recovery time between large draw-offs (such as baths), and helps to
increase system efficiency (especially with older boilers). High performance
cylinders often have improved factory-applied insulation as well.
11
Section 4 - Systems and components
Figure 7: Unvented hot water system
Hot water taps
when high pressure is needed at the outlet eg for showers. It is therefore
important to ensure that the incoming water supply pressure and flow to
the dwelling are adequate and that all showers have the hot and cold water
supply at the same nominal pressure.This eliminates the need for a shower
pump.
Cold water taps
Table 1: Domestic hot water flow rates
System type
Instantaneous combi
Cold water main
Storage combi
2,3
Thermal store
3
Unvented storage
Vented storage
Unvented cylinders are increasingly used in new systems.These operate at
mains pressure.They employ an internal expansion facility or a dedicated
external expansion vessel, and do not require a feed cistern in the loft.
1,3
low
Flow rate
medium
x
x
x
x
x
x
x
x
x
x
x
2,3
4
high
Notes:
1 rarely applied to oil-fired boilers and depends on boiler heat output; less satisfactory for two or
more simultaneous draw-offs
2 depends on boiler heat output and storage capacity
3 depends on adequate mains water supply
4 requires high level feed cistern
Figure 8:Thermal storage system
4.3 Upgrading systems
Feed and
expansion cistern
Hot water
taps
Many existing wet central heating systems are poorly controlled and of
obsolete design. Poor design features which fail to meet Best Practice
requirements include:
gravity circulation to the hot water cylinder, which results in stored
water being slow to re-heat;
lack of cylinder thermostat, resulting in excessive stored water
temperature;
lack of room thermostat (rooms are too hot);
lack of TRVs, causing excessive room temperatures and poor system
balancing;
absence of boiler interlock, causing the boiler to stay hot and to cycle
unnecessarily during programmed periods.
•
•
Cold water
main
•
•
•
When upgrading, use the CHeSS specifications (see Section 6).
Most hot water cylinders and thermal stores are supplied with factoryapplied insulation and these should always be used in preference to
cylinders with separate jackets. Cylinders should satisfy British Standards
(27,28,29).
Medium-duty cylinders have inferior performance and do not meet CHeSS
basic requirements or those of the building regulations, and so should not
be used for either new or replacement installations.
Thermal stores can be obtained that hold water at high temperatures,
heated by the boiler directly.These are available for ‘hot water only’ or ‘hot
water and space heating’.
Mains-fed systems such as combi boilers, unvented cylinders and thermal
stores can supply hot water at mains pressure.This is extremely beneficial
12
4.4 Flue types
Most new boilers installed will be of the condensing type and in most cases
they will be replacing non-condensing units.The different flue arrangements
of the existing model may affect the siting of the new boiler. Figure 9 shows
typical flue types found in existing systems.
Section 4 - Systems and components
•
Figure 9: Existing flue types
Air
•
•
Flue
•
Flow
Air
Extended and vertical flues are available for many condensing boilers
using concentric ducts. In some cases these allow flue lengths of over
5m, with a number of bends. Concentric extended flue options are
available for horizontal and vertical applications (see Figure 10).
Low level balanced flues must not be used with boilers fired by gas-oil
fuel.
New boilers will all have fan-assisted pressure jet burners, but the
existing unit may use a vaporising burner.
Rooms containing existing open-flue boilers will normally have a
purpose-made vent to ensure sufficient air for combustion. However,
this is unlikely to be required if the replacement is a room-sealed
boiler (32).
Room-sealed
balanced flue
Return
Open
flue
Figure 10: Extended flues
Flow
Low level horizontal concentric
AIR
Return
The following is a list of important factors to consider when replacing a
non-condensing boiler with a condensing unit.
New oil-fired boilers are very efficient and operate with comparatively
low flue-gas temperatures. A correctly sized, well-constructed, lined flue
is essential for efficient performance.
The flue must be correctly designed and sized using suitable, corrosion
resistant materials and it must be provided with a suitable terminal (32).
Most, but not all, new condensing boilers are room-sealed with a
balanced flue. Room-sealed boilers do not require special provision for
combustion air in that room but compartment ventilation may be
required for cooling purposes (32).
Boilers with open flues should, when possible, be located in a separate
boiler room where combustion air is taken directly from the outside. If
it is to be installed in a regularly used room such as a kitchen, advice
should be sought from the manufacturer.
The plume will be visible for much of the time the boiler is in use and
can sometimes cause a nuisance. For this reason, special consideration
should be given to the siting of the new flue terminal (see Section 9.2).
•
Vertical concentric
•
•
•
•
High level horizontal concentric
13
Section 4 - Systems and components
4.5 Heat emitters
4.6 Circulator pumps
A wide range of heat emitters are available (see Table 2). Radiators remain
the most popular type and modern versions are usually slightly smaller for
an equivalent heat output. Many modern radiators also have a smaller water
content, making for a faster warm-up.
A circulator pump must be selected with sufficient design pressure and flow
rate for the total system resistance when operational. If the pump is
undersized or is set too low, the flow may be inadequate to meet the
manufacturer’s minimum requirement.This will result in the boiler operating
with a larger temperature rise than intended. On the other hand, a pump
that is larger than required will result in excessive water velocity noise as
well as unnecessary electricity consumption.
The heat output of the radiators should be carefully calculated (19). All
radiators should be fitted with a TRV (see CHeSS) excluding those in a
room with a controlling room thermostat.
Underfloor heating is an attractive alternative in the right circumstances,
but it needs to be installed by specialists. It also requires careful control in
accordance with the manufacturer’s guidance.
Other important points regarding heat emitters include the following.
Radiators sited under windows counteract cold downdraughts and so
give a more comfortable environment in the room.
Radiators should be installed close to the floor, preferably 100-150mm
above finished floor level.
Wide, low radiators will be more effective at heating the room evenly
than tall, narrow ‘designer’ styles.
Enclosures around radiators reduce the heat output.
•
•
•
Circulator pumps are built into combi and system boilers and it must be
ensured that the pump has adequate head and flow rate to meet the
system design.
Pumps that are installed separately (ie not supplied as part of the boiler
unit) and that have automatic speed control should only be used in heating
systems with TRVs if the design of the pump and system ensures that the
minimum flow rate through the boiler (as specified by the boiler
manufacturer) is certain to be maintained under all conditions. If a pump
with automatic speed control is used in a system with an automatic bypass,
ensure that the minimum water flow rate (as specified by the boiler
manufacturer) can be maintained under all operating conditions.
•
Multiple pumps (one for each water circuit) may be used as an alternative
to a single pump with motorised valves, provided that each water circuit
has a non-return valve. Advice on pump sizing can be obtained from the
British Pump Manufacturers’ Association (BPMA) website at
www.bpma.org.uk
Table 2: Heat emitters
14
Type
Comment
Panel radiator
The most common type in modern housing. Available in a wide range of outputs and sizes.
‘Compact’ radiator
A radiator or convector fitted with top grille and side covers.
‘Column’ and ‘designer’ radiators
Available in a wide range of colours and shapes.
Low Surface Temperature (LST) radiator
Safe option where young children or the elderly may be at risk. Limited to a surface temperature of
43°C in order to prevent injury.
Towel rail
For towel warming and will give some heat to the bathroom.
Fan convector
Wall hung and ‘kickspace’ units available.These provide a more rapid heating response.They need an
electrical supply and there may be some fan noise.
Underfloor heating coils
Requires specialist installation and controls. May be less suitable for rooms requiring only intermittent
heating.
Section 5 - Controls
Installing effective controls can have a major impact on the energy
consumption of heating and hot water systems.This section describes the
types of controls now available and outlines which are most appropriate for
different heating systems.
5.1 Individual controls
Effective controls will increase operating efficiencies, especially when older
systems are being updated.They also provide the householder with the
opportunity to minimise energy consumption by ensuring the right comfort
temperatures are maintained and so reducing overheating. Reducing room
temperatures will also save energy (see panel).Timed space and water
heating periods will also help to avoid excessive use of energy. Heating fuel
is expensive (oil-fired boilers typically consume 25-50 pence of fuel an hour
when operating) and reducing the firing time will make a proportionate
difference to running costs.
The controls listed here are normally installed separately from the boiler
although some may be incorporated within it. For clarity of specification,
Appendix C contains a full list of controls including those often fitted
within appliances and gives industry-agreed definitions.
What is a ‘good’ control system? It is one which ensures the boiler does
not operate unless there is a demand and that only provides heat where
and when it is needed in order to achieve the required temperatures.The
selection of appropriate controls plays a key part in minimising the overall
running costs of a heating or hot water system.
Programmer - This can switch two circuits separately (usually heating
To maximise the efficiency of a heating system, control standards must
meet Best Practice. However, in order just to achieve the SEDBUK
efficiency claimed for a boiler, at least the basic set of controls given in
CHeSS must be installed (see Section 6).
•
The cost benefit of controls should not be underestimated. Upgrading the
controls on older heating systems can save up to 18 per cent on energy
bills, for example when a full set of controls is fitted to a system which
previously had none.This is important, as over 80 per cent of the energy a
householder uses in the home is for space and hot water heating.
VAT on heating controls
Heating controls for domestic wet central heating systems are
recognized by the Government as an energy efficiency measure.VAT is
therefore charged at a lower rate - currently five per cent instead of
the full rate of 17.5 per cent.This lower rate applies to both equipment
and installation costs, but only when the work is carried out by an
installer registered for VAT.
Energy savings from good controls
Installing a minimum standard of controls on a system which
previously had none can reduce fuel consumption and CO2
emissions by 18 per cent.
Reducing higher than necessary room temperatures will cut energy
use.Turning down the room thermostat by 1°C will reduce space
heating consumption by 6-10 per cent.
An easy to use programmer that is adjusted to match the
householder’s occupancy pattern helps reduce wasteful heating
when no one is at home.
This section describes the range of controls commonly used in oil-fired
systems, what they do and why they are important.
In the following listing, Best Practice controls are noted.
Time Switch - A simple time control that will only switch one circuit. It
should be chosen so that it is easy to understand and reset, especially when
there is a change to the householder’s domestic routine.
and hot water).There are three basic types:
a mini-programmer allows space heating and water to be on together,
or hot water alone but not heating alone;
a standard programmer uses the same time settings for space heating
and hot water;
a full programmer allows fully independent time setting for space and
hot water heating.
•
•
Room thermostat - A simple room temperature control. Most room
thermostats include an accelerator or anticipator, which has the effect of
smoothing out the temperature cycle so that on and off periods are not
too long.Wireless units that provide increased flexibility in positioning and
eliminate visible wiring are now available (see note on page 17 regarding
wireless controls).
Programmable room thermostat (Best Practice) - This allows
different temperatures to be set for different periods of the day or week
and so can provide a good match to householder living patterns,
particularly if occupancy varies.This device also has a ‘night setback’ feature
where a minimum temperature can be maintained. Many of these models
are battery-operated and can replace a conventional thermostat without
the need for additional cabling. Some versions also allow time control of
hot water provision.
Figure 11: A programmable room thermostat
offers greater flexibility in setting temperatures
and times than a standard room thermostat,
producing greater savings
•
Room
temperature
•
Z
Z
Z Z
Z
•
Early
morning
Mid-morning
Afternoon
Evening
Night
15
Section 5 - Controls
Cylinder thermostat (Best Practice) - A simple control of stored
electrical power from the programmable room thermostat (or separate
programmer and room thermostat) and the cylinder thermostat will
drive the valve motor to the open position. Once the motor is fully
open, the end switch will close and electrical power is then passed to
the boiler (and pump). Once the power to the valve is removed
(programmer off-period, or thermostat is satisfied) the end switch will
open and the boiler and pump will stop.
hot water temperature, usually strapped to the side of the hot water
cylinder. It is commonly used with a motorised valve to provide close
control of water temperature.
Frost thermostat - A simple override control used to prevent frost
damage to the dwelling and/or boiler system.The frost air thermostat
should be fitted in a suitable place within the dwelling to ensure a minimum
temperature is always maintained.
Pipe thermostat - Where the boiler is installed in an unheated area
such as a garage, a pipe thermostat should be fitted to the exposed
pipework.This is in addition to the frost air thermostat and is designed to
prevent the boiler from firing unnecessarily in cold weather and so wasting
fuel. If the boiler incorporates its own frost thermostat, a separate pipe
thermostat is normally not required.
•
•
Regular boiler with ‘dual head’ pump.The dual head unit includes a
dedicated wiring centre which ensures that boiler interlock is achieved.
Where separate pumps are used, advice from the manufacturer is
needed in regard to the correct use of relays, check valves, etc.
Combi boiler.This only requires a room thermostat connection to provide
interlock as hot water delivery is controlled directly by the boiler.
A boiler energy manager may need a different wiring arrangement, achieving
interlock by an alternative method.
Thermostatic radiator valve (TRV) (Best Practice) - TRVs are
used to limit the temperature in individual rooms.They also prevent
overheating from solar and other incidental gains. In this way, they cut down
on unnecessary consumption. Programmable units, which can be timed to
switch on and off, are also available.
Figure 12: Boiler interlock in a system with two,
2-port valves (this shows the general logic and
should not be interpreted as an installation
instruction, as the actual wiring will depend on
the particular products used).
Thermostatic hot water temperature limit valve - These selfacting valves without motors are used to limit hot water temperature in
domestic hot water cylinders. Some units sense primary water (boiler)
temperature, others have a separate remote sensor for stored water
temperature. Cylinder controls should not be used with these unless they
also operate an electrical switch to provide boiler interlock. Otherwise the
boiler will cycle unnecessarily.
Neutral
230 V
End switch
HW motorised
valve
HW
SH
Boiler
Motorised valve (Best Practice) - These control water flow from the
boiler to heating and hot water circuits.Two-port valves can also be used
to provide zone control eg. allowing lower temperatures to be set for
sleeping areas or different heating times. An explanation of the different
types is given in Appendix D. Multiple pumps are an alternative to
motorised valves (see Section 4.6).
wiring arrangement to prevent the boiler firing when there is no demand
for heat.The boiler is ‘interlocked’ when it is switched on and off by
thermostats containing electrical switches. All thermostats in the heating
system fitted with electrical switches should be wired in this way.This
includes room thermostats, programmable room thermostats, cylinder
thermostats and some types of boiler energy managers. In many cases, the
interlock is also applied to the operation of the pump, although any
requirements for pump overrun stipulated by the boiler manufacturer must
be observed. Without interlock, a boiler is likely to cycle on an off
regularly, wasting energy by keeping hot unnecessarily.
Achieving interlock depends upon the boiler type and the controls fitted.
Typical examples of boiler interlock are as follows.
Regular boiler with one 3-port or at least two 2-port motorised valves.
The interlock is usually arranged so that the room or cylinder
thermostat switches the power supply to the boiler (and sometimes the
pump) through the motorised valve ‘end’ switches. In other words,
•
16
End switch
Pump
SH motorised
valve
Repeat for each additional heating zone
Boiler interlock (Best Practice) - This is not a device, but rather a
Cylinder
thermostat
Programmable
room thermostat with
timing for hot water
Programmable room
thermostat for each
additional space
heating zone
End switch
SH
SH motorised valve
for each additional
space heating zone
Automatic bypass valve (Best Practice) - This controls water flow
according to the pressure of the water across it. It is used to maintain a
minimum flow rate through the boiler and to limit the circulation pressure
when alternative water paths are closed. A bypass circuit must be installed if
the boiler manufacturer requires one, or specifies that a minimum flow rate
has to be maintained while the boiler is firing.The installed bypass circuit
must then include an automatic bypass valve, not a fixed position valve.
The use of an automatic bypass is important where the system includes a
large number of TRVs.When most of these are open, the automatic bypass
Section 5 - Controls
remains closed, allowing the full water flow to circulate around the heating
system. As the TRVs start to close, the automatic bypass starts to open,
maintaining the appropriate water flow through the boiler. It is also likely to
reduce noise in the system caused by excess water velocity.
Wireless controls
Wireless controls should be designed with adequate immunity to
blocking by other radio transmissions. If not, they may become
unreliable or cease to work as nearby radio frequency bands become
increasingly used for mobile phones and other communication services.
See CHeSS Note 12 in Appendix B for details on how to specify
wireless controls.
An automatic bypass is always preferable to a fixed bypass.With a fixed
bypass, there is a constant flow of hot water coming out of the boiler,
which is fed directly into the return at all times.This means that the boiler
operates at a higher temperature, reducing efficiency and restricting the
amount of heat transferred to the system.
It is very important that both automatic and fixed bypasses are correctly
adjusted. Poor adjustment will give rise to increased boiler return
temperatures and reduced boiler efficiency.
Particular care is required when selecting a pump with automatic speed
control for a system with an automatic bypass. It is important to ensure
that the boiler manufacturer’s minimum recommended water flow rate is
maintained under all operating conditions.
Boiler energy manager - These are self-contained devices which have
a number of the functions found in other individual controls described in
this section.They usually have a number of control functions including
weather or load compensation and sometimes optimum start, frost
protection, night setback, anti-cycling control and hot water override.Table
3 lists a range of control functions which may be included.
5.2 Selecting controls
The minimum sets of controls consistent with satisfactory heating system
performance are those listed as basic in the CHeSS specification (see
Section 6). However, it is recommended that the Best Practice level is
followed. Figures 13 and 14 show Best Practice for combi and regular boiler
systems.
New systems must always be fully pumped and existing semi-gravity
systems (ie with gravity circulation to the hot water cylinder) should be
converted. Published boiler efficiencies cannot be achieved unless the whole
system is fully pumped and effectively controlled.
Table 3: Control functions commonly built into boilers and control units
Compensator
Reduces boiler water temperature for space heating according to internal/external air temperature. It
should increase the efficiency of condensing boilers by reducing the average water temperature of the
system.
Delayed start
Reduces energy use by delaying boiler start time when the weather is mild.
Optimum start
Adjusts the heating start time to give the required dwelling comfort temperature at a chosen time
Night setback
Allows a low temperature to be maintained at night, providing improved comfort and reduced warm-up
time in the dwelling in cold weather. In this way it can reduce the risk of hypothermia. A programmable
room thermostat can fulfil this function.
Self-adaptive function
Reduces appliance ‘on’ time by learning from previous temperature characteristics.
Anti-cycling control
Delays boiler firing in order to reduce cycling frequency, but is unlikely to produce significant energy
savings (33). In some circumstances consumption may be reduced, but normally at the expense of
performance or comfort. Standalone units (ie those not supplied as part of the boiler) are not generally
recommended as they provide little or no improvement over the basic level of control detailed in CHeSS
Figure 13: Best Practice schematic for combi systems
Hot water
Mains water
Best Practice - Combi boilers
Programmable room
thermostat
Cylinder thermostat
TRVs on all radiators except in
rooms with a room thermostat
Automatic bypass valve
Boiler interlock
•
•
•
•
•
17
Section 5 - Controls
Figure 14: Best Practice schematic for regular
boiler systems (the programmable room
thermostat must have an additional hot water
timing capability)
Systems that provide multiple zone control are now available which allow
time and temperature control of individual rooms or multiple zones, thereby
providing more effective and efficient heat distribution in the dwelling.
Weather compensation - As external temperatures rise, so a weather
compensating function reduces average water circulation temperature (see
Figure 16). Greatest benefit is achieved with condensing boilers.
Figure 16:Weather compensation
Best Practice - Regular boilers
Programmable room thermostat with additional hot water timing
capability
Cylinder thermostat
TRVs on all radiators except in rooms with a room thermostat
Automatic bypass valve
Boiler interlock
•
•
•
•
•
Delayed/optimum start - During mild weather, heat-up times are
reduced. A delayed start function takes advantage of this. An optimum start
control varies the start time to ensure the dwelling only reaches the
desired temperature when the householder needs it (see Figure 17). Room
thermostats with a delayed start function are now available.
5.3 Further control
improvements
Figure 17: Delayed/optimum start function
Potential energy
savings
Zone control - CHeSS Best Practice and basic options already include
zone temperature control, achieved using TRVs. If zones are to be
independently time controlled as well, it will usually be necessary to install
additional room thermostats and a two-port motorised valve (this is to
allow the programmer to shut off water circulation).The wiring in such
situations must be arranged so that boiler interlock works in all zones.
Internal temperature (C)
20
Typical settings
Time switch
set for 6am
16
12
Optimised/
delayed
start
8
Figure 15: Zone controls
5
6
7
8
9
10
Time (hours)
Zone control is particularly beneficial in larger, poorly insulated buildings.
Building Regulations in England and Wales require that no zone is larger
than 150m2 in floor area and each zone should be capable of independent
time and temperature control.
18
Home automation - Whole house control systems are now available,
integrating the operation and control of a wide range of systems and
appliances. Of particular relevance for energy efficiency are:
time and temperature control of individual rooms;
features to permit remote setting and operation of time switches, ie
programmers and thermostats;
feedback for the householder on energy use, which can encourage
energy efficiency.
•
•
•
Section 6 - Central Heating System Specifications (CHeSS)
CHeSS provides a series of ready-made specifications for purchasing the
components that critically affect the energy efficiency of wet central heating
systems. Following them will improve energy efficiency and reduce carbon
emissions. Purchasers should use these specifications to ensure their
heating installations will meet Best Practice or basic requirements. Installers
can use them to quote for systems of defined quality, comparable with
those of their competitors.
specification is available in a separate Energy Efficiency Best Practice in
Housing document (18).That publication also contains quantified energy,
carbon and cost savings for the different specifications.
The basic specifications HR5 and HC5 are sufficient to comply with the
building regulations.The two Best Practice specifications HR6 and HC6 are
to be preferred (see overleaf).
The main elements are reproduced in the following tables and the
explanatory notes can be found at the end of this document.The complete
Basic (2005)
Reference
CHeSS - HR5 (2005)
Description
Domestic wet central heating system with regular boiler and separate hot water store.
• A regular boiler (not a combi) which has a SEDBUK efficiency of at least:
Boiler
(see notes 5 and 6)
Hot water store
- 86% if fuelled by natural gas (bands A and B);
- 86% if fuelled by LPG (bands A and B);
- 85% if fuelled by oil (bands A and B, and some from band C).
EITHER
• Hot water cylinder, whose heat exchanger and insulation properties both meet or exceed (see note 7) those of the
relevant British Standards (see Refs [7] , [8]).
OR
• Thermal (primary) storage system, whose insulation properties meet or exceed those specified in Ref[ ].
• Full programmer.
• Room thermostat.
• Cylinder thermostat.
• Boiler interlock (see note 13).
• TRVs on all radiators, except in rooms with a room thermostat.
• Automatic bypass valve (see note 14).
9
Controls
(see notes 10, 11 and 12)
Installation
See notes 1, 2, 3 and 4.
Basic (2005)
Reference
CHeSS - HC5 (2005)
Description
Domestic wet central heating system with combi or CPSU boiler.
Boiler
(see notes 5 and 6)
Hot water store
Controls
(see notes 10, 11 and 12)
Installation
• A combi or CPSU boiler which has a SEDBUK efficiency of at least:
- 86% if fuelled by natural gas (bands A and B);
- 86% if fuelled by LPG (bands A and B);
- 82% if fuelled by oil (bands A to C).
None, unless included within boiler.
• Time switch.
• Room thermostat.
• Boiler interlock (see note 13).
• TRVs on all radiators, except in rooms with a room thermostat.
• Automatic bypass valve (see note 14).
See notes 1, 2, 3 and 4.
In the CHeSS specifications reproduced above, the notes referred to have been placed in Appendix B of this guide.
19
Section 6 - Central Heating System Specifications (CHeSS)
Recommended Best Practice (2005)
Reference
CHeSS - HR6 (2005)
Description
Domestic wet central heating system with regular boiler and separate hot water store.
• A regular boiler (not a combi) which has a SEDBUK efficiency of at least:
Boiler
(see notes 5 and 6)
Hot water store
- 90% if fuelled by natural gas (band A);
- 90% if fuelled by LPG (band A);
- 90% if fuelled by oil (band A).
EITHER
• High-performance hot water cylinder (see note 8).
OR
• High-performance thermal (primary) storage system (see note 9).
In suitable buildings, consideration should be given to fitting a cylinder with an additional heat exchanger to allow for
solar water heating.
Controls
(see notes 10, 11 and 12)
• Programmable room thermostat, with additional timing capability for hot water.
• Cylinder thermostat.
• Boiler interlock (see note 13).
• TRVs on all radiators, except in rooms with a room thermostat.
• Automatic bypass valve (see note 14).
More advanced controls, such as weather compensation, may be considered, but at present cannot be confirmed as
cost effective.
Installation
See notes 1, 2, 3 and 4.
Recommended Best Practice (2005)
Reference
CHeSS - HC6 (2005)
Description
Domestic wet central heating system with combi or CPSU boiler.
Boiler
(see notes 5 and 6)
Hot water store
Controls
(see notes 10, 11 and 12)
•
A combi or CPSU boiler which has a SEDBUK efficiency of at least:
- 90% if fuelled by natural gas (band A);
- 90% if fuelled by LPG (band A);
- 86% if fuelled by oil (bands A and B).
None, unless included within boiler.
• Programmable room thermostat.
• Boiler interlock (see note 13).
• TRVs on all radiators, except in rooms with a room thermostat.
• Automatic bypass valve (see note 14).
More advanced controls, such as weather compensation, may be considered, but at present cannot be confirmed as
cost effective.
Installation
See notes 1, 2, 3 and 4.
In the CHeSS specifications reproduced above, the notes referred to have been placed in Appendix B of this guide.
20
Section 7 - Energy efficiency
The information in this guide is designed to improve the energy efficiency
of dwellings. Selecting the most energy efficient boilers suitable for the
particular application is vital. Several factors need to be considered when
choosing a boiler:
The best source of SEDBUK figures is the Boiler Efficiency Database (see
Section 7.5).Where this is not available, purchasers should look for this
standard form of words in manufacturers’ literature:
•
•
•
“Seasonal efficiency (SEDBUK) = [x]%
The value is used in the UK Government’s Standard Assessment Procedure
(SAP) for energy rating of dwellings.The test data from which it has been
calculated have been certified by [name and/or certification of Notified
Body].”
seasonal (ie annual in-use) efficiency;
typical heating and hot water running costs for the dwelling(s);
typical CO2 emissions for space and water heating.
Minimising demand
Whilst this guide aims to improve heating and hot water systems
through careful selection of boilers and controls, it is important to
remember that other factors affect the overall energy efficiency of the
dwelling. In particular, it is essential to minimise:
fabric heat loss through walls, floors, roofs and windows;
ventilation heat loss from windows, unused chimneys and cracks or
gaps in the structure of the dwelling.
•
•
Energy efficiency figures calculated by other methods may not be consistent
with SEDBUK - and should be disregarded.
Figure 18 shows typical SEDBUK efficiencies for both new and older
boilers. In practice there are limits both to the minimum efficiency due to
the requirements of the Boiler Efficiency Directive, and to the maximum
permitted value based on theoretical considerations.
Figure 18:Typical SEDBUK values for different
boiler types
7.1 Comparing boiler
efficiencies
SEDBUK ranges for oil boilers
Regular (pre-1985)
The term ‘boiler efficiency’ needs some explanation since there are many
values that may be quoted, and these are calculated in different ways. In any
comparison of the efficiency of alternative products, it is essential to ensure
that the same method is being used.
Regular (pre-1998)
Combi (pre-1998)
Regular (new)
The efficiency value now used in the Government’s Standard Assessment
Procedure and in the building regulations is known by the acronym
SEDBUK, (Seasonal Efficiency of a Domestic Boiler in the UK). SEDBUK
represents the best estimate presently available of overall seasonal in-use
boiler efficiency for space heating and hot water in UK dwellings. It is used
throughout this guide as well as in CHeSS, the Energy Saving Trust’s ‘Energy
Efficiency Recommended’ scheme, and other programmes designed to
promote efficient boilers.
A boiler’s SEDBUK efficiency is an indicator of the average annual boiler
efficiency determined by the amount of heat delivered to the primary (boiler
water) heating circuit. It is assumed that the boiler is installed in a fullypumped system which has been correctly designed and which has adequate
controls.The claimed SEDBUK efficiency level will not be achieved otherwise.
The SEDBUK calculation process (which can be found in Appendix D of the
SAP (26)) uses actual boiler test data, the measurements being taken by
methods defined in European standards to meet the requirements of the
European Boiler Efficiency Directive (20).This provides manufacturers with
an incentive to make their products as efficient as possible.
As SEDBUK has been designed specifically for SAP energy rating purposes,
it takes account of heat losses associated with space and water heating. It
does not, however, include surface heat losses from any hot water store
within or external to the boiler.These are treated separately as they may
provide a small amount of useful heat to the dwelling during the heating
season.This is important when comparing products, as stores with high
heat losses will increase annual energy consumption but do not affect
SEDBUK values.
Combi (new)
Condensing regular
50
54
58
62
66
70
74
78
82
86
90
94
98
Efficiency %
7.2 The Standard Assessment
Procedure (SAP)
Home energy ratings are designed to give an indication of the energy
efficiency of a dwelling and so allow householders to compare different
homes.The SAP is the Government’s chosen rating system and indicates
the running costs of space and water heating.The building regulations
procedures require all new dwellings to be assessed in this way.
The current version of SAP is SAP 2001. SAP 2005 is under development
and will be introduced at the end of 2005. In SAP 2001, ratings are
expressed on a scale of 1-120, with higher figures representing greater
efficiency and lower running costs.The actual figure depends on certain
characteristics of the building and its heating systems, in particular:
building design;
insulation levels;
solar heat gains;
ventilation;
heating and hot water efficiency (SEDBUK) and controls.
•
•
•
•
•
21
Section 7 - Energy efficiency
7.3 Energy consumption and
running costs
7.5 The Boiler Efficiency
Database
Table 4 gives typical annual fuel costs for some of the more common types
of dwelling found in the UK - both existing properties and new buildings.
Existing housing is typical of the existing housing stock (35). New housing
has the same floor areas for comparison, but is built with insulation levels
that would satisfy the latest building regulations.The flat is on the top floor
(a top floor flat has an energy consumption intermediate between a ground
and mid-floor flat). Hot water costs are related to a typical number of
occupants for the size of property.
The Boiler Efficiency Database (25) is an independently authenticated record
of the efficiency of most gas and oil-fired domestic boilers in the UK. Most
of the data in it can be viewed at the website www.boilers.org.uk. Both
current and obsolete boilers are included and the database is updated
regularly, with a new edition issued each month. For heating installers, a
printed extract from the database is published at intervals by the Energy
Saving Trust under the title The Little Blue Book of Boilers.
Figures shown assume average UK weather conditions (the Midlands).
Consumption would be around 3-6 per cent lower in the south and 3-6
per cent higher in the north.
Typical energy consumption has been calculated using the Building Research
Establishment (BRE) Domestic Energy Model, BREDEM-12 (34).This estimates
annual domestic energy usage associated with house design, insulation levels,
local climate and type of heating system (including efficiency and heating
usage).The model is widely used for calculating domestic fuel running costs.
Fuel costs of 1.63 pence per kWh are taken from the 2001 edition of the
SAP (Table 12).These costs do not include standing charges, maintenance or
circulating pump running costs.
7.4 Carbon dioxide emissions
Table 5 gives typical values of annual CO2 emissions for the same types of
dwelling. Carbon intensity values are taken from SAP (2001) Table 15.
For boilers currently on sale, the database gives SEDBUK efficiency figures
derived from independently certified tests and the corresponding efficiency
band (see panel). Manufacturers send details of their products to the
database manager, who checks that efficiency test results have been
independently certified by an approved testing organisation and then
calculates SEDBUK figures for the database entry. For obsolete boilers,
where certified test results may not be available, a generic efficiency for the
type of boiler concerned is quoted instead of SEDBUK.
As a simple guide to efficiency, SEDBUK values are divided into seven
bands, from A (most efficient) to G (see panel on next page).The entries
for each boiler on the database give the banding which may be used on
product literature and labels, although there is no requirement to do so.
In addition to the database, the website also has two interactive programs.
The first is an annual fuel cost estimator for boilers of known efficiency in
different types of housing.The second is a whole-house boiler sizing
calculator to help estimate a suitable boiler size for individual properties
where dimensions and other relevant data are known.
Table 4: Annual fuel (oil) costs for heating and hot water in different property types
EXISTING HOUSING
Type of oil boiler
Regular (pre- 1985)
Regular (pre- 1998)
Combi (pre- 1998)
Regular (new)
Combi (new)
Condensing regular (new)
NEW HOUSING
SEDBUK
Flat
Bungalow
Terraced
Semidetached
Detached
Flat
Bungalow
Terraced
Semidetached
Detached
65%
75%
75%
85%
82%
93%
£232
£201
£201
£178
£184
£162
£304
£263
£263
£232
£241
£212
£317
£274
£274
£242
£251
£221
£359
£311
£311
£274
£284
£251
£508
£441
£441
£389
£403
£355
£58
£60
£53
£73
£75
£66
£73
£75
£66
£91
£94
£83
£108
£112
£99
Table 5: CO2 emissions (tonne/yr) for oil heating and hot water in different property types
EXISTING HOUSING
Type of oil boiler
Regular (pre- 1985)
Regular (pre- 1998)
Combi (pre- 1998)
Regular (new)
Combi (new)
Condensing regular (new)
22
NEW HOUSING
SEDBUK
Flat
Bungalow
Terraced
Semidetached
Detached
Flat
Bungalow
Terraced
Semidetached
Detached
65%
75%
75%
85%
82%
93%
3.85
3.33
3.33
2.94
3.05
2.69
5.03
4.36
4.36
3.85
3.99
3.52
5.24
4.55
4.55
4.01
4.16
3.66
5.94
5.15
5.15
4.54
4.70
4.15
8.42
7.30
7.30
6.44
6.68
5.88
1.37
1.42
1.25
1.72
1.79
1.58
1.72
1.79
1.58
2.15
2.22
1.96
2.55
2.64
2.33
Section 7 - Energy efficiency
SEDBUK range
7.6 Saving energy with better
controls
Band
90% and above
A
86% - 90%
B
82% - 86%
C
78% - 82%
D
74% - 78%
E
70% - 74%
F
Below 70%
G
It is better to replace both boiler and controls when upgrading a heating
system. However, in some circumstances, it may be appropriate to leave an
existing boiler in place and upgrade the controls. Table 6 shows what
savings could be obtained by fitting new controls (to CHeSS standards) to
older types of boiler.
Table 6: Typical energy savings achievable by upgrading the controls on existing systems
Approximate average savings2
(% of the existing fuel consumption)
Add the following for
‘Best Practice’ controls:
Existing system has the
following controls:
Older Boiler with gravity DHW
b
b
3
b
b
18%
13%
b
12%
4%
b
10%
Older Boiler - Fully pumped4
b
b
b
17%
10%
4%
b
9%
Older Combi Boiler4
b
b
b
15%
7%
4%
NOTES
1. All improved systems must include a programmable room thermostat (replaces existing room thermostat).
2.These are average savings assuming normal controls, systems and user behaviour. Actual savings may be significantly different.The savings only apply where an older-type boiler is fitted. It is assumed that the
SEDBUK (see7.1) is 60% for the Gravity DHW system and 68% for the fully-pumped and combi systems.
3.This option provides only a partial interlock (hot water only)
4. All improved systems should include an automatic bypass valve if a bypass circuit is necessary (see Appendix B note 14)
Room thermostat
b
Boiler interlock
Programmable thermostat
TRVs on most radiators
Cylinder thermostat
Motorised valve
23
Section 8 - System selection: practical issues
When choosing which Best Practice system to install the following
questions should be addressed.
1. Which boiler type is most appropriate?
2. What size boiler is required?
3. Where will the boiler be positioned?
4. What will be the flue terminal position and arrangement?
5. Where does the condensate drain go?
6. What are the arrangements for the oil tank and oil supply?
7. Are there any special ventilation requirements
8. Will it be an open or sealed system?
9. What type of hot water system is most appropriate?
10. What type and size of heat emitters are required?
11. What controls are needed?
CHeSS (see Section 6) specifies the main components needed to achieve
Best Practice in wet central heating systems, but there are many additional
aspects of the installation to consider.The following tables outline the key
points.
8.1 Which type of boiler is most appropriate? (36,39)
Regular or combi?
Best Practice regular boilers (see CHeSS HR6) provide most flexibility in system design. A combi (see
Chess HC6) incorporates some system equipment which reduces installation time. Oil-fired condensing
combis are being introduced.
Condensing or non-condensing?
Use condensing types as specified in CHeSS HR6 or HC6 only.These provide significantly higher
efficiency than non-condensing types, although they do require connection to a drain as well as particular
care in sitting the flue terminal. Condensing boilers must be installed in England and Wales from 1 April
2007 unless an exception is allowed (see panel in Section 2.1.2).
Combi hot water performance
The maximum flow rate at the hot water tap will depend on the boiler’s heat output, the design of the
draw-off pipe and the capacity of the internal hot water store. Combis usually take more time to fill a
bath than a conventional storage system.
Cooker boilers and back boilers
These are not recommended as they are not currently available in condensing versions. Back boilers are
only available in open-flue models and usually include an integral electric fire in front.
Large boilers
For boilers with output greater than 50kW, refer to suitable publications at www.thecarbontrust.co.uk.
8.2 What size boiler is required? (19,39)
24
Maximum load
The boiler needs to be sized to meet the maximum load expected on the system: this includes the heat
used by the emitters, the hot water system and the pipework.
New systems
A full design heat loss method should be employed to identify the most appropriate boiler. An example
can be found at www.centralheating.co.uk.
Boiler replacements
Size for size replacement is not recommended. Insulation levels may have been improved or the original
sizing may have been incorrect. Heating and hot water requirements should be re-checked before a new
boiler is chosen. Oversizing will result in lower efficiency and unnecessary capital costs. An interactive
procedure for correctly sizing boilers up to 25kW can be found at www.boilers.org.uk.
Combis
Power rating is normally determined by hot water requirements and there is generally more than
enough heat output for space heating. This should always be checked in large and/or poorly insulated
dwellings.
Section 8 - System selection: practical issues
8.3 Where will the boiler be positioned? (19,21,36,39)
General issues
Exception: is it difficult to install a
condensing boiler?
If an exception is being considered, follow the exceptions procedure (see panel in Section 2.1.2) before a
boiler position is considered.
Space
It has to be adequate for the boiler type (including flue pipe space).
Access
It needs to be sufficient for installation, maintenance and servicing.
Flue position
Can a flue be fitted easily? Is an extended horizontal or vertical flue required, and will angled flue bends
be necessary? See Section 8.4.
Condensate drain
Is there a suitable adjacent drain point? See Section 8.5.
Location?
- heated area
Preferred, saves energy.
- unheated area
Requires frost protection. Consider externally mounted boiler.
- understairs
There are special requirements in this case regarding the height of the building (maximum 2 stories); fire
resistance; whether it is intended to use it as a storage area as well; instruction notices; and the provision
of a self-closing door.
- bathroom, shower room,
sleeping room
There are regulations regarding electrical work in bath and shower rooms. Open-flue boilers must not
be installed where they can draw combustion air from a bathroom or bedroom. Room-sealed boilers
should not be installed in sleeping areas if avoidable.
- roofspace, loft, attic
This option should only be considered in exceptional circumstances.The local fire authority and house
insurers will need to be notified.The weight of the boiler, the provision of ventilation and safe access
must all be taken into account.
- fireplace
Condensing back boilers (BBU) are not currently available.Where boilers are located inside a living
space, particular consideration must be given to the position of the flue, the air supply routes and the
provision of suitable condensate drainage.
- garage
Frost protection will be required. Only room-sealed models are permitted in Northern Ireland.
- basements and cellars
Ensure a practical connection to a drain point is available - consider using a condensate pump.
8.4 What will be the flue terminal position and arrangement? (32,38)
Condensing boilers
Plume
A plume is present most of the time that the boiler operates. Avoid terminal positions where a plume
would be directed:
• towards or across a door or window;
• towards a frequently used area (eg. patio, access route or car parking space);
• across a neighboring dwelling or boundary;
• in close proximity to an opposite wall or surface.
Freezing
Avoid situations where:
condensate from a terminal may drip onto a path, then freeze and cause a hazard;
the plume may condense then freeze, damaging a wall or surface.
•
•
Terminal guards
Usually required where terminal is less than 2m from ground level.These need to withstand corrosive
effect of condensate.
Extended flues
If the plume may cause a nuisance, consider an extended vertical/horizontal flue or alternative boiler
position.
25
Section 8 - System selection: practical issues
8.5 Where does the condensate drain go? (38)
Boiler position
Ensure the chosen drain point can be reached from the proposed boiler position.
Drain points
Condensate can be drained to:
an internal stack pipe;
a waste pipe;
an external drain, gully or rainwater hopper;
a purpose-made soakaway.
•
•
•
•
Boiler condensate siphons
Check whether the chosen boiler has a fitted condensate siphon. If not, externally situated condensate
pipework is more likely to freeze in cold weather.
Condensate traps
Check whether the chosen boiler has an internal condensate trap with a water seal greater than 75mm.
If not, an air-break and additional trap with a seal greater than 75mm must be installed.
Pipework
All pipework must have a fall of 2.5 degrees and be securely clipped. External runs must not exceed 3m
and be insulated. Corrosion resistant pipe materials (not copper or steel) must be used.
Pipe sizes
Where there is no manufacturer’s guidance:
pipes in a heated area should have a nominal diameter of at least 22mm;
externally run pipes should have a nominal diameter of at least 32mm.
•
•
Condensate pumps
If gravity will not take the condensate to the drain point (for example if the boiler is situated in a
basement) a condensate pump will need to be considered.
8.6 What are the arrangements for the oil tank and oil supply?
Building regulations
There are mandatory requirements for the installation of oil storage tanks and supply systems. It is
essential to refer to the building regulations and to OFTEC guidance. Note that requirements differ
around the UK.
Oil tanks (refer to OFTEC website
www.oftec.org)
Type - Tanks are generally made from steel or plastic. Integrally bunded (see below) and underground
units are also available.
Sizes - This choice will depend on the rated output of the boiler and the likely frequency of fuel
deliveries.
Position - There are mandatory fire protection requirements covering the minimum distance of tanks
from buildings and boundaries. At the same time, there needs to be good access for deliveries, inspection
and maintenance.
Base - This must be fireproof and larger than the tank’s ‘footprint’.
Bunding - It is a mandatory requirement to carry out an assessment on whether bunding is needed to
satisfy environmental protection safeguards.Written proof of this assessment must be maintained. A
standard risk assessment form (TI/133) is available from OFTEC which will indicate whether secondary
containment can be omitted.
Oil supply pipework (refer to OFTEC
website www.oftec.org)
This can be installed above or below ground. It should be sleeved and protected against damage.The
choice of gravity or suction supply will depend on the relative heights of tank and burner.The position
of the tank fuel outlet (top or bottom) will affect the arrangement of the pipes. A remote sensing fire
valve must be fitted in the pipeline outside the dwelling.The sensor must be located higher than the
level of the burner. An oil filter should be fitted in the oil supply line.
8.7 Are there any special ventilation requirements? (32,36)
26
Room sealed
Room-sealed balanced-flue appliances do not require special provision for room ventilation. Open-flue boilers need a purposemade, correctly-sized, non-closable air vent to ensure that there is sufficient air for combustion. Special provision may be required
where an extract fan is fitted.
Compartment
Some boilers may require purpose made ventilation when a boiler is fitted in a compartment.
Section 8 - System selection: practical issues
8.8 Will it be an open or sealed system? (19, 36)
Sealed
Commonly used in new systems, especially with combis and all system boilers.They incorporate an
expansion vessel.The system pressure rises with temperature.The necessary additional safety controls
are normally incorporated as part of the boiler. It is important to check that this expansion vessel has
enough capacity for the whole installed system.
Open
Typical of existing installations, these systems require an expansion cistern which must be at the highest
point in the system.
8.9 What type of hot water system is most appropriate?
Mains fed (combis, unvented cylinders,
thermal stores, CPSUs)
Ensure that water supply to the dwelling (both pressure and flow rate) is adequate (with both hot and
cold water running).The flow rate obtainable from an instantaneous combi will also depend on its
maximum heat output.
Storage systems
Cylinders meeting current Best Practice standards use high recovery coils and are well insulated. It is no
longer permitted to install ‘medium-duty’ cylinders, which have inferior performance. Ensure existing hot
water cylinders are well insulated. Cylinders of 117-140 litre capacity are usually adequate for smaller
households with a single bathroom (19).
Unvented storage
These are mains fed and usually give a high hot water flow rate at high pressure (29).
Thermal storage
These are also mains fed and will provide a high hot water flow rate at high pressure (30).
Vented storage
This type needs a cold water cistern and will usually provide a high hot water flow rate at low pressure
(27,28).
Solar systems
In suitable properties (especially those with an unobstructed south-facing roof), solar water heating
systems can make a significant contribution to the hot water energy requirements, and save boiler fuel.
A hot water cylinder with an additional coil for connection to the solar collector system is necessary. If
solar water heating is likely to be installed in the near future, it is advisable to choose a suitable cylinder
at the time the main heating system is installed, as it will save cost and disruption later. Separate
guidance and advice on solar water heating should be sought (50).
8.10 What type and size of heat emitters are required? (19, 36)
Heat emitter type
Panel radiators offer the lowest cost option. Use Low Surface Temperature (LST) radiators where young
children or elderly are likely to be present and may be at risk.
Size
Avoid undersizing as it will result in unsatisfactory heating performance and may give rise to reduced
boiler efficiency from excessive boiler cycling. Use a full design heat loss calculation method. An example
can be found at www.centralheating.co.uk.
When used with condensing boilers
Increasing radiator sizes can reduce average boiler operating temperatures and therefore increase
efficiency. However, care should be exercised when oversized radiators are installed in a room with a
controlling room thermostat. If radiators in other rooms are not similarly oversized, the controllability
of the whole system may be affected.
27
Section 8 - System selection: practical issues
8.11 What controls are needed? (18,19)
Best Practice
Use Best Practice controls wherever possible.
• Regular boilers use a programmable room thermostat with separate timing capability for hot
•
28
water. All systems should be fully pumped, have both room and cylinder thermostats, use motorised
valves or multiple pumps, and have separate zones for heating and hot water.They should also have
TRVs, an automatic bypass valve and a boiler interlock.
Combi boilers use a programmable room thermostat,TRVs and boiler interlock. Install an automatic
bypass valve if the manufacturer advises that a bypass should be fitted.
Basic
The basic CHeSS specification is the minimum acceptable standard.The system should include a full
programmer (a time switch for combis). All other controls as for Best Practice.
Thermostatic Radiator Valves (TRVs)
TRVs must be installed on all radiators except in rooms with a room thermostat. An automatic bypass
valve must be installed if the manufacturer’s instructions require one or if a minimum flow rate has to
be maintained while the boiler is firing.
Pumps
Advice on pump selection is available from www.bpma.org.uk. See Section 4.6 for pumps with automatic
speed control.
Systems with gravity hot water
These must be converted to fully pumped to comply with Best Practice requirements.
Very large dwellings
These should be divided into separate zones not exceeding 150m2 in floor area. Each zone should be
capable of independent time and temperature control.
Frost protection
This should always be considered for both the dwelling and the central heating system.
Other controls
Additional controls can also be beneficial (see Section 5.3).
Section 9 - Installing central heating systems
9.1 ‘Competent person’
requirements
Figure 19: Statutory minimum distances
for terminal siting
Opening
window
In England and Wales, installation details of oil-fired heating systems, oil-fired
combustion appliances, oil storage tanks and the pipes connecting them,
must be made available to OFTEC. OFTEC will then send a copy of the
certificates to the householder and to the local authority Building Control
Department. An individual registered under the Oil Firing Registration
Scheme run by OFTEC is deemed competent to install oil-fired equipment
and can undertake this work. Alternatively installers or their customers can
use the local authority Building Control route for notification, for which a
charge is made.
B
A
Pathway
C
Opposite
boundary
Other parts of the United Kingdom are considering the adoption of similar
arrangements.
A – minimum distance 600mm – may be a nuisance if it
'wets' opposite boundary, crosses main pathway or
condensate can drip on pathway.
B – minimum distance 600mm – may be a nuisance as
plume could obscure window.
C – minimum distance 600mm – may be a nuisance if plume
crosses door.
All installations of unvented hot water systems must be carried out by a
‘competent person’ who is approved by an appropriate body.
9.2 Installing the boiler
While condensing boilers can normally be installed in a similar location to
non-condensing units, additional factors need to be considered:
the plume from the flue terminal should not cause a nuisance;
there must be a convenient drain point for the condensate.
•
•
The plume should not cross:
a frequently used access route;
any frequently used area (such as a patio or car parking space);
a neighbouring dwelling.
•
•
•
Nor should it be directed towards a window or door, or be sited close to a
facing wall or other surface.
Where a boiler, particularly a replacement unit, is being installed inside a
dwelling it may not be appropriate to site it in the same location. Even
where it is, extended flue options may have to be considered as well as the
practicalities of finding (and connecting to) a suitable drain point.Where
there are particular difficulties with installing a condensing boiler, a boiler
exception can be considered (see panel in Section 2.1.2). Even if an
exception is allowed, a condensing boiler should always be considered due
to increased efficiency and lower running costs.
•
Flue terminal position
•
•
Condensing boilers will produce a visible plume of water vapour for a
significant proportion of their operating time.To avoid this causing a
nuisance, a vertical flue can remove the plume to a high level.
There are also other aspects to consider when planning the flue terminal
position.
A free passage of air is needed at all times to aid plume dispersal which may be difficult in sheltered locations.
In cold weather, the condensate could cause a safety hazard if it freezes
on pathways, or if it results in frost damage to surfaces.
The plume could trigger infra-red security lighting if sited in the wrong
place.
Ensure terminals do not obscure security camera field of vision.
The terminal guards must be able to resist corrosive properties of the
condensate.
•
•
Condensate drain point
At low level, the plume may be a nuisance. Minimum statutory distances
from terminals to obstacles (such as opposite walls) are shown in Figure 19,
although in some cases these may still not be sufficient. Some boilers eject
flue gases horizontally in a powerful jet which may not disperse for a
considerable distance. Refer to building regulations (22,23,24) which show all
minimum statutory distances from flue terminals.
Refer to the condensing boiler exceptions procedure before the boiler/flue
terminal position is decided. In any event particular care is required where
it is intended to fit a flue terminal which will be positioned less than 2.5m
from a facing wall, boundary fence or neighbouring property.Where the
plume from a terminal may cause a nuisance, consider an extended vertical
or horizontal flue or moving the boiler to an alternative position which may
provide a more acceptable terminal position.
The amount of condensate produced by a condensing boiler depends upon
a number of factors but four litres a day is not unusual.The liquid is slightly
acidic (about the same as tomato juice, a pH value of between three and
six) and must be disposed of correctly. Suitable drain points include:
•
•
•
•
an internal stack pipe;
a waste pipe;
an external drain or gully;
a rainwater hopper that is part of a combined system (ie sewer carries
both rainwater and foul water);
a purpose-made soakaway.
Internal drain points are to be preferred as they are less likely to become
blocked by leaves, or by frozen condensate (38).
•
29
Section 9 - Installing central heating systems
Installing the condensate drain pipe
Condensate traps - Building regulations require a trap to be installed in the
condensate pipe from the boiler:
if this goes straight to a gully or rainwater hopper, a water seal of at
least 38mm is required;
if connected to another waste pipe, the water seal must be at least
75mm to prevent foul smells entering the dwelling.
•
•
Internal traps already fitted within the boiler may not always satisfy the
building regulations. Unless otherwise stated by the manufacturer’s
instructions, an additional trap of either 38mm or 75mm (depending on the
proposed connection) will be required. An air break between the traps is
also necessary (see Figure 20).
Pipe runs - These should be as short as possible. If a condensate drainpipe
runs outside the dwelling, this external run should be restricted to a
maximum of 3m in order to reduce the risk of freezing. If the boiler is
installed in an unheated space such as a garage, all the condensate
drainpipes should be regarded as ‘external’.
Pipe slope - A minimum of 2.5 degrees away from the boiler.
effect of the condensate, such as the plastics recommended for condensate
pipes.
A trap with a minimum condensate seal of 75mm is required.The boiler
may incorporate a trap of this size, if not one will have to be fitted to the
condensate drainpipe. A visible air break is required between this and any
other trap.
For single dwellings up to three stories high, the condensate drainpipe
should discharge into the stack at least 450mm above the invert of the tail
of the bend at the foot of the stack. If this point is not visible, then the
height should be measured from the bottom of the lowest straight section
of stack to be seen.This height should be increased for buildings of more
storeys.
The stack connection should not cause cross flow into any other branch
pipe, nor should it allow flow from that branch into the condensate pipe.
This can be ensured by maintaining an offset between branch pipes of at
least 110mm on a 100mm diameter stack, or 250mm on a 150mm stack.
Figure 20: Condensate trap options
Bends - These should be kept to a minimum. Similarly, the number of fittings
or joints outside the dwelling needs to be minimised in order to reduce the
risk of condensate being trapped.
Internal trap
> 75* mm
Air break
Additional trap
> 75* mm
Fixings - These must be sufficient to prevent sagging. A maximum spacing of
0.5m for horizontal and 1.0m for vertical sections is recommended.
Pipe sizes - Follow the boiler manufacturer’s instructions. In the absence of
such guidance:
the minimum nominal diameter for internal pipe runs is 22mm;
a larger diameter (at least 32mm nominal diameter) is required for
externally run pipes to reduce the risk of freezing.
•
•
Internal trap
> 75* mm
* If the drain is connected
directly to an external gully
or hopper then use 38mm
Pipe materials - These should be resistant to the acid condensate.The
plastics used for standard wastewater plumbing systems and cistern
overflow pipes are suitable. Copper or mild steel pipes and fittings must
not be used.
Condensate siphons - Many boilers have a siphon fitted as part of the
condensate trap arrangement.This intermittently discharges the
condensate, reducing the risk of freezing where part of the pipework runs
externally. If the boiler does not include a siphon, avoid external pipework
as far as possible.Where necessary it should have a minimum nominal
diameter of 32mm.
Pipe slope
>21/2 deg
Figure 21: Condensate connection to
an internal stack
Internal trap
>75mm
Condensate pumps - These may be considered where the boiler is in the
basement or a drain point cannot be reached by gravity. Pump
manufacturers’ instructions must always be followed.
>110mm
(for 100mm stack)
Pipe slope
>21/2 deg
Condensate drain termination
Connecting to an internal stack - This is the preferred method of
connection.The stack must be made of a material resistant to the corrosive
30
Branch pipe
> 450mm
(for up to 3 floors)
100mm Internal stack
Section 9 - Installing central heating systems
Connecting to an external stack - In addition to the requirements detailed
above, care must be paid to reducing any risk of the drain blocking due to
the condensate freezing.The length of pipe external to the dwelling should
be kept as short as possible and certainly less than 3m.Traps in the
drainpipe must be inside the building. In exposed locations, the pipe should
be protected with waterproof insulation.
Connecting to an internal waste pipe - The most convenient (and most
frequently used) method of connection is via an internal discharge branch
to a kitchen sink, washing machine or dishwasher drain. It can be connected
up- or down-stream of the relevant waste trap and if practical should be
mounted onto the top of the pipe. If connected upstream of the waste trap
an air break is necessary between this trap and the boiler’s own trap.This is
usually provided by the sink waste pipe itself, as long as the sink has an
integral overflow (see Figure 22).
If, on the other hand, the condensate drain is connected downstream of the
sink (or other appliance) waste trap, and the boiler does not have an
integral trap with a seal of at least 75mm, an additional trap with that seal
must be fitted. An air break must be included between the traps (see Figure
23). In either case the trap and airbreak should be above the level of the
sink to prevent flows into the boiler or airbreak.
located as close as possible to the boiler but clear of the building
foundations and not in the vicinity of other services such as gas, electricity
or water connections.The position and presence of a soakaway must be
taken into account when carrying out a risk assessment for installation of
an oil storage tank.The external pipework must be kept to a minimum and
not more than 3m in length.The pipe may be taken below or above the
ground level.
Figure 24 shows a suitable soakaway design (see also Part H3 of Approved
Document H of the Building Regulations).The size of the soakaway will
depend to a large extent on the soil conditions. Unlike the case of a
rainwater soakaway, the soil does not have to accommodate large water
volumes over short periods. A soakaway approximately 200mm in diameter
and 400mm deep (with limestone chippings) will normally be sufficient.
Figure 23: Connection to an internal sink waste
(downstream of sink trap)
Internal trap
>75mm
It is preferable to connect to a washing machine drain rather than a kitchen
sink.This reduces the likelihood of solid waste and fats blocking or
restricting the condensate drain entry point.
Connecting to an external drain point - If the condensate cannot be
drained via an internal route, then direct connection to an external gully or
rainwater hopper can be considered. A rainwater hopper must be
connected to a combined system (i.e. sewer carries both rainwater and foul
water).The open end of the pipe should be below the grid level but above
the water level in the gully or hopper. Condensate must not be disposed of
in ‘grey water’ systems.
Height above
sink >100mm
SINK
Pipe slope
>21/2 deg
Connecting to a soakaway - If none of the previous solutions are possible
then a purpose made soakaway can be used.The soakaway should be
Figure 22: Connection to an internal sink waste
(upstream of sink trap)
Figure 24: Possible configuration for a
condensate soakaway drain
> 500mm
>1000mm
Alternative ground level
Height above
sink >100mm
SINK
Ground level
Section of plastic
drain pipe
Holes in side away
from dwelling
Limestone
chipping fill
31
Section 9 - Installing central heating systems
9.3 Controls
There are a number of points to be considered when installing commonlyused central heating controls.
Cylinder thermostat
CHeSS Best Practice specification
This control is usually strapped onto the cylinder about one third of the
way up from the base.The strap needs to be tight to ensure good thermal
contact and be adjusted to about 60°C. If set too high, it may result in
scalding, but if too low it can increase the risk of legionella bacteria which
could result in serious health problems (36,37).
Programmable Room Thermostat
CHeSS Best Practice specification
If fitted with a regular boiler, this must have a hot water timing capability. In
larger dwellings, where separate time/temperature zones are required, only
one programmable room thermostat needs this hot water timing capability.
A programmable room thermostat should be located in a regularly heated
area.While free movement of air is important, it should be mounted away
from draughts, internal heat sources and direct sunlight. It should not be
fitted in a room where supplementary room heating (such as electric
heaters or open fires) can affect it. So do not site one in a kitchen or
combined kitchen and living room. Only install one in a main living room if
it is certain that no supplementary heating is used there. Appropriate
positions would be in the hall or a living room without supplementary
heating.
The unit should be readily accessible to the householder, not hidden away
in a cupboard or behind furniture. It should be located at a height of about
1.5m above floor level unless the occupants include wheelchair users. In this
instance a suitable height in excess of 1m should be agreed with the
homeowner.
Motorised valve
CHeSS Best Practice specification
The most common types of motorised valves are two- and three-port.
How each will be used depends on pipework layout and preference - as
displayed in the following examples.
Three-port valves can provide separate heating and hot water circuits;
most three-port units feature a mid-position which allows shared flow.
Where there is more than one heating zone, as well as a hot water
zone, use a separate two-port valve for each zone.
Valves of 22mm can be used on boilers up to around 20kW. Beyond
that, 28mm or larger should be used.
•
•
•
Note: motorised valves must not be positioned in the line of the open
safety vent pipe or the feed-and-expansion pipe.
Thermostatic Radiator Valve (TRV)
CHeSS Basic and Best Practice specifications
Time switch/programmer
CHeSS basic systems only
Time switches can only switch one circuit (such as combi heating), while
programmers can control two (eg. heating and hot water). Ensure that the
unit is appropriate.
These controls should be installed where they can be easily reached, read
and altered. Do not fit them in places inconvenient for the householder (eg.
in an airing cupboard).
Room thermostat
CHeSS basic systems only
Installation considerations are the same as for the programmable room
thermostat.
32
TRVs must be used in systems meeting either specification.They should be
installed in all rooms except those in which a controlling room thermostat
provides a boiler interlock. Many TRVs can be fitted on the flow or return
to the radiator and many are bi-directional. If not, the direction of the
water flow must be taken into account when installing them.
Automatic bypass valve
CHeSS Basic and Best Practice specifications
These should be used for systems meeting either specification unless the
boiler manufacturer does not require a bypass circuit be fitted to ensure a
minimum flow rate.The valve should be installed between the boiler
primary flow and return, taking account of the direction of flow.
Ensure that the valve has adequate flow capacity. It should be set so as
ensure adequate flow through the boiler when all motorised valves and/or
TRVs close.
Section 9 - Installing central heating systems
Frost protection
(air and pipe thermostat)
Where both air and pipe thermostats are used, the contacts should be
wired in series from a live supply* that is not switched by a
timeswitch/programmer or thermostats.This ensures that protection is
available 24 hours a day. Some boilers already include their own frost
protection, but the level of protection for the whole dwelling needs to be
considered.
•
•
•
* for units that require thermostats with voltage-free contacts, refer to the
manufacturer’s instructions.
be sleeved and protected against damage (45).The choice of gravity or
suction supply will depend on the relative heights of tank and burner
(40,46) Also see manufacturer’s instructions for further guidance.The
position of the tank fuel outlet (top or the bottom) will affect the
arrangement of the pipes.
Fire valve - This should be remote sensing and fitted outside the dwelling
in the oil supply pipework. Note that the remote sensor must be fitted
above the level of the appliance’s burner.
Oil filter - This should be installed in the oil supply line.
Tank gauge - This should be fitted on the tank (manual gauges) or
remotely positioned (electronic) in a convenient to read location.
9.5 Water treatment
Weather compensator or unit with external sensor
The external sensor should be positioned on a north-facing wall, away from
direct sunlight and other heat sources.
9.4 Oil storage and supply
The installation of oil storage tanks and supply pipework is subject to
building regulations in the different parts of Great Britain (42,49).The relevant
building regulations in Northern Ireland are currently under review.
Environmental legislation that affects this is in force in England and Wales
(43), being drafted in Scotland (48), and being reviewed in Northern Ireland.
Detailed guidance is set out in BS 5410 Part 1 1997(32) and more details are
available from OFTEC.
Three types of water treatment should be considered:
cleaning and flushing of the system before use;
corrosion inhibition;
softening the water supply in the case of combi boilers to prevent
excessive scaling of the heat exchanger (particularly important in hard
water areas).
•
•
•
Damage may be caused by inappropriate treatment so the boiler
manufacturer’s instructions should always be followed. Cleaning is essential
for both new and replacement systems and (if recommended by the boiler
manufacturer) a suitable chemical cleaning agent can be used.When a boiler
is replaced, it is essential to drain and flush all the old water from the
system in case it contains a corrosion inhibitor unsuitable for the new
boiler. More advice is available on water treatment, the need for it, methods
and dealing with problems (36,37).
The key considerations are as follows.
Size of tank - The amount of oil to store will depend both on boiler size
and the expected frequency of fuel deliveries. OFTEC recommendations
(40) are given in the table below.
Tank position - Domestic oil storage tanks of up to 3500 litres should be
mounted on a fireproof base at least 300mm larger than the tank in all
directions.The tank must be a minimum of 1.8m from a building and
760mm from a boundary. If these conditions cannot be achieved,
additional fire protection will be needed (32). Larger tanks face more
stringent requirements (32,44).
Accessibility - The tank must be located so that there is good access for
deliveries, inspection and maintenance.Where possible, it should be
visible from the delivery tanker and be less than 30m from the tanker
stand.
Bunding - A bund is a secondary containment system. It should be
capable of holding 110 per cent of the maximum tank contents in the
event of leakage, overfilling or spill. Oil tanks of up to 2,500 litres serving
a single family private dwelling may not need bunding - a risk assessment
must be carried out to confirm this. Risk assessment forms are available
from OFTEC (41).
•
•
•
•
• Supply pipework - This can be installed above or below ground. It should
33
Section 10 - Commissioning and handover
10.1 Commissioning
For safe and energy-efficient operation, all parts of a new central heating
and hot water system need to be checked to ensure they are working
properly. In particular:
the boiler and system should be cleaned using a recognised flushing
procedure;
the burner should be adjusted for optimum combustion and thereby
maximum efficiency;
the key system components such as gauges, valves, fire valves, burner
and system controls must be checked for correct and safe operation;
controls should be set to their optimum settings;
the customer should be instructed on how to operate the controls, and
the importance of regularly servicing the system needs to be made
clear.
•
•
•
•
•
•
why it is best to switch space and water heating off when not required;
why it is best to turn the room thermostat down to frost protection
levels (approximately 12°C) unless a separate frost protection system
has been fitted;
that sealed boiler systems must have adequate system pressure and
what to do if re-pressurising is needed;
operational and safety aspects of the oil storage and supply system,
including how to use the tank contents gauge, and the necessary
arrangements for re-filling.
•
•
•
In England and Wales, OFTEC Registered Technicians who carry out this
work must send details of to OFTEC who will send certificates to the
householder and the local authority Building Control. Alternatively installers
or their customers can use the local authority Building Control route for
notification. Other parts of the UK are considering similar arrangements.
10.2 Advising householders
Installers must instruct the householder how to set and use the controls
properly and effectively. In particular, the operation of programmers can be
difficult to understand and homeowners will gain little or no benefit from
an incorrectly set device. In fact, they will probably end up wasting energy.
As a bare minimum, the manufacturer’s instructions should be left with the
householder. However, it will usually be necessary to demonstrate:
how to set the programmer clock and adjust for GMT and BST;
the use of the time control override function;
how to set summer hot water only;
how to separate space heating and domestic hot water time settings
(regular boilers only);
how to set room and cylinder thermostats;
how to set TRVs.
•
•
•
•
•
•
The installer will also need to explain:
the function of room thermostats and TRVs (for example, that they
should be left alone once set, rather than used as on/off switches);
that the cylinder thermostat needs to be left at approximately 60°C,
since setting it higher may result in scalding while setting it lower can
allow the growth of legionella bacteria;
that the radiator lockshield and automatic bypass valve should not be
adjusted once set by the installer;
•
•
•
34
10.3 Servicing
Users should be made aware of the importance of regular servicing - both
of the boiler and the system as a whole (including the oil supply system).
This will help maintain its safety and efficiency. In particular, users should
consider taking out a regular service contract where a competent service
engineer (registered with OFTEC) will clean and maintain the boiler as well
as checking the operation of the system and controls.
Appendix A - Exception procedure flowchart
Figure 25: Exception procedure flowchart
Start
Is it difficult
to install a condensing
boiler in this
building?
Is it
possible to install a
condensing boiler in
this building?
Complete
the form and
declaration
Complete the form
for installation
option with lowest
assessment score
Does
total assessment
score (box T) show that
installation is
uneconomic?
Customer willing
to install a condensing
boiler anyway?
Install non-condensing
boiler, in position
chosen by customer
Install condensing
boiler, in position
chosen by customer
35
Appendix B - Notes to CHeSS 2005
CHeSS is published in full as ref(18) and reproduced here in Section 6
1. Other components: The specifications list only the principal
components of a heating system affecting energy efficiency. Other
components will be required, such as radiators, circulator pumps (see
Note 4), cisterns (feed and expansion tanks), and motorised valves. All
components must be selected and sized correctly.
2. Design and installation: Heating systems should be designed and
installed in accordance with relevant safety regulations, manufacturers’
instructions, the Benchmark scheme (see Ref[10]), building regulations
(see Refs[1], [2], [11]), and British Standards (see Refs[12], [13]). More
detailed advice on domestic wet central heating systems is given in the
government’s Energy Efficiency Best Practice Programme in Housing
good practice guides (see Refs[3], [4]), and Ref[5]. In England and Wales
commissioning and handover of information on operation and
maintenance is a requirement of Building Regulations Part L1 (see Ref[1])
and a suitable commissioning certificate is published as part of
Benchmark (see Ref[10]).
3. Water treatment: Three types of water treatment should be
considered - (a) cleaning and flushing of the system before use; (b)
corrosion inhibition, and (c) softening of the water supply to combi
boilers for hot water service in hard water areas. In each case the
recommendation of the boiler manufacturer must be followed as damage
may be caused by unsuitable treatment. For both new and replacement
systems, cleaning is essential and, if recommended in the boiler
manufacturer’s instructions, a suitable chemical cleaning agent can be
used.When a boiler is replaced it is essential to drain and flush all old
water from the system lest it contains a corrosion inhibitor unsuitable
for the new boiler. Advice on the need for treatment is given in clauses
26 and 38 of BS 5449 (see Ref[12]), and on causes of problems and
methods of treatment in BS 7593 (see Ref[14]).
4. Circulator pump: Advice on pump dimensioning is available from the
BPMA (British Pump Manufacturers’ Association) website at
www.bpma.org.uk Pumps installed separately from the boiler (not
supplied as part of the boiler unit) which have automatic speed control
should not be used in heating systems with TRVs unless the design of the
pump and system ensures that the minimum flow rate through the boiler
(as specified by the boiler manufacturer) is certain to be maintained
under all conditions.
5. Boiler size and type: The whole house boiler sizing method for houses
and flats gives guidance on boiler size and is available on the website
www.boilers.org.uk.
A regular boiler does not have the capability to provide domestic hot
water directly, though it may do so indirectly via a separate hot water
store.
A combination (combi) boiler does have the capability to provide
domestic hot water directly, and some models contain an internal hot
water store.
A combined primary storage unit (CPSU) is a boiler with a burner
that heats a thermal store directly.
Each of these may be either a condensing or non-condensing boiler, and
condensing boilers are always more efficient. Gas and LPG boilers in the
CHeSS specifications HR5 and HC5, and all boilers in HR6 and HC6, are
condensing boilers. From April 2005, Building Regulations Part L1 in
England & Wales require all new gas boilers to be condensing, whether
36
installed in new or existing housing, unless there are exceptional
circumstances that would make the installation impractical or excessively
costly. Condensing boilers are fitted with a drain to dispose of the liquid
condensate.
For further definitions of boiler types see Appendix D of Ref[6].
6. Boiler efficiency: SEDBUK (Seasonal Efficiency of Domestic Boilers in
the UK) is the preferred measure of the seasonal efficiency of a boiler
installed in typical domestic conditions in the UK, and is used in SAP
assessments and the building regulations.The SEDBUK efficiency of most
current and obsolete boilers can be found on the website
www.boilers.org.uk. Although SEDBUK is expressed as a percentage, an
A to G scale of percentage bands has also been defined (see Section 7 of
the guide).
For gas boilers, the distinction between bands A and B is small, and
standard tests do not measure the difference reliably. Consequently, it is
not cost effective to purchase band A rather than band B unless the
additional cost is low
7. Hot water cylinder (basic): Vented cylinders shall comply with
BS 1566:2002 (see Ref[7]). Unvented cylinders shall either comply with
BS 7206 (see Ref[8]) or be approved by the BBA or other equivalent
body. All cylinders must be factory insulated such that the standing heat
loss will not exceed 1.6 x (0.2 + 0.051 V2/3) kWh per 24 hours, where V is
the capacity in litres.This is equivalent to about 0.8 watt per litre for the
popular 117 litre cylinder.
8. Hot water cylinder (high performance): A high performance cylinder may
be either vented or unvented.The manufacturer must confirm that the
heat exchanger and insulation properties exceed the requirements of the
relevant British Standards (see Refs[7], [8]) as follows:
(i) The standing heat loss must not exceed 1.28 x (0.2 + 0.051 V2/3)
kWh per 24 hours, where V is the capacity in litres.This is
equivalent to about 0.64 watts per litre for the popular 117 litre
cylinder.
(ii) For vented cylinders the re-heat time for a capacity of 117 litres and
above as measured in BS 1566: 2002 shall not exceed 20 minutes.
Cylinders below 117 litres shall have a proportionately lower re-heat
time (eg. not more than 10 minutes for a 58.5 litre cylinder).
(iii) The re-heat performance of unvented cylinders should be tested
and certified using the procedure in BS 7206 (see Ref[8]) by the
BBA or other third party.With a 15 litres/minute primary flow rate,
the re-heat time for cylinders of 120 litres and above shall not
exceed 20 minutes. Cylinders below 120 litres shall have a
proportionately lower re-heat time (eg. not more than 10 minutes
for a 60 litre cylinder).
(iv) For unvented cylinders tested with a 20 litres/minute primary flow
rate (as per the Water Research Centre Procedure), the re-heat
time for cylinders of 120 litres and above shall not exceed 17.5
minutes. Cylinders below 120 litres shall have a proportionately
lower re-heat time (eg. not more than 8.75 minutes for a 60 litre
cylinder).
Solar-compatible cylinders contain an additional heat exchanger for
connection to a solar water heating system.They offer the opportunity
to install a solar water heating system at greatly reduced cost and with
less disruption in the future.
Appendix B - Notes to CHeSS 2005
CHeSS is published in full as ref(18) and reproduced here in Section 6
9 Thermal store (high performance): A high-performance thermal
(primary) storage system must have insulation properties exceeding by
at least 15 per cent those given in the WMA Performance Specification
for Thermal Stores (see Ref[9]), and comply with the Specification in
other respects.
10.Circuits and zones: Systems with regular boilers must have separately
controlled circuits to the hot water cylinder and radiators, and both
circuits must have pumped circulation. Large properties must be divided
into zones not exceeding 150 m2 floor area, so that the operation of the
heating in each zone can be timed and temperature controlled
independently.
11. Definitions of heating controls are given in Ref[4].The most common
are repeated below.
A time switch is an electrical switch operated by a clock to control
either space heating or hot water, or both together but not
independently.
A full programmer allows the time settings for space heating and hot
water to be fully independent.
A room thermostat measures the air temperature within the building
and switches the space heating on and off. A single target temperature
may be set by the user.
A programmable room thermostat is a combined time switch and
room thermostat which allows the user to set different periods with
different target temperatures for space heating, usually in a weekly cycle.
Some models also allow time control of hot water, so can replace a full
programmer.
A cylinder thermostat measures the temperature of the hot water
cylinder and switches the water heating on and off.
A TRV (thermostatic radiator valve) has an air temperature sensor
which is used to control the heat output from the radiator by adjusting
water flow.
thermostat. In a system with a regular boiler it can be achieved by
correct wiring interconnection of the room thermostat, cylinder
thermostat, and motorised valve(s). It may also be achieved by more
advanced controls, such as a boiler energy manager.TRVs alone are not
sufficient for boiler interlock.
14.An automatic bypass valve controls water flow in accordance with
the water pressure across it, and is used to maintain a minimum flow
rate through the boiler and to limit circulation pressure when alternative
water paths are closed. A bypass circuit must be installed if the boiler
manufacturer requires one, or specifies that a minimum flow rate has to
be maintained while the boiler is firing.The installed bypass circuit must
then include an automatic bypass valve (not a fixed-position valve). Care
must be taken to set up the automatic bypass valve correctly, so as to
achieve the minimum flow rate required (but not more) when alternative
water paths are closed.
12.Wireless controls should be designed with a satisfactory level of
immunity to blocking by other radio transmissions. Otherwise they may
become unreliable, or cease to work, as nearby radio frequency bands
become increasingly heavily used for mobile phone and other
communication services.
Compliance with the essential requirements of the European Radio and
Telecommunications Terminal Equipment (RTTE) Directive 1999/5/EC is
insufficient, as the directive is designed only to ensure that wireless
products do not cause harmful interference to other transmissions. It
does not give any assurance that the product has a satisfactory level of
immunity to interference from other radio transmissions.
Consequently it is not sufficient for the manufacturer to confirm
compliance with the RTTE Directive.The manufacturer should also
confirm that the switching range (and preferably alignment range) do not
include any frequencies below 430 MHz, and that in regard to ETSI EN
300 220-1 v1.3.1 (see Ref[15]) the receiver classification (clause 4.1.1) is
either Class 1 or Class 2, and the device is marked in accordance with
clause 4.3.4..
13.Boiler interlock is not a physical device but an arrangement of the
system controls (room thermostats, programmable room thermostats,
cylinder thermostats, programmers and time switches) so as to ensure
that the boiler does not fire when there is no demand for heat.
In a system with a combi boiler it can be achieved by fitting a room
37
Appendix C - Definitions of boiler types
As given in SAP Appendix D (26)
B1.1 Boiler
A gas or liquid fuelled appliance designed to provide hot water for space
heating. It may (but need not) be designed to provide domestic hot water
as well.
B1.2 Condensing boiler
A boiler designed to make use of the latent heat released by the
condensation of water vapour in the combustion flue products.The boiler
must allow the condensate to leave the heat exchanger in liquid form by
way of a condensate drain. ‘Condensing’ may only be applied to the
definitions B1. 3 to B1. 14 inclusive. Boilers not so designed, or without the
means to remove the condensate in liquid form, are called ‘non-condensing’.
B1.3 Regular boiler
A boiler which does not have the capability to provide domestic hot water
directly (i.e. not a combination boiler). It may nevertheless provide
domestic hot water indirectly via a separate hot water storage cylinder.
B1.4 On/off regular boiler
A regular boiler without the capability to vary the fuel burning rate whilst
maintaining continuous burner firing.This includes those with alternative
burning rates set once only at time of installation, referred to as range
rating.
B1.5 Modulating regular boiler
A regular boiler with the capability to vary the fuel burning rate whilst
maintaining continuous burner firing.
B1.6 Combination boiler
A boiler with the capability to provide domestic hot water directly, in some
cases containing an internal hot water store.
B1.7 Instantaneous combination boiler
A combination boiler without an internal hot water store, or with an
internal hot water store of capacity less than 15 litres.
B1.8 On/off instantaneous combination boiler
An instantaneous combination boiler that only has a single fuel burning rate
for space heating.This includes appliances with alternative burning rates set
once only at time of installation, referred to as range rating.
B1.9 Modulating instantaneous combination boiler
An instantaneous combination boiler with the capability to vary the fuel
burning rate whilst maintaining continuous burner firing.
B1.10 Storage combination boiler
A combination boiler with an internal hot water store of capacity at least
15 litres but less than 70 litres,
OR
a combination boiler with an internal hot water store of capacity at least 70
litres, in which the feed to the space heating circuit is not taken directly
from the store. If the store is at least 70 litres and the feed to the space
heating circuit is taken directly from the store, treat as a CPSU (B1. 13 or
B1. 14).
B1.11 On/off storage combination boiler
A storage combination boiler that only has a single fuel burning rate for
38
space heating.This includes appliances with alternative burning rates set
once only at time of installation, referred to as range rating.
B1.12 Modulating storage combination boiler
A storage combination boiler with the capability to vary the fuel burning
rate whilst maintaining continuous burner firing.
B1.13 On/off combined primary storage unit (CPSU)
A single appliance designed to provide both space heating and the
production of domestic hot water, in which there is a burner that heats a
thermal store which contains mainly primary water which is in common
with the space heating circuit.The store must have a capacity of at least 70
litres and the feed to the space heating circuit must be taken directly from
the store.The appliance does not have the capability to vary the fuel
burning rate whilst maintaining continuous burner firing.This includes those
with alternative burning rates set once only at time of installation, referred
to as range rating.
B1.14 Modulating combined primary storage unit (CPSU)
A single appliance designed to provide both space heating and the
production of domestic hot water, in which there is a burner that heats a
thermal store which contains mainly primary water which is in common
with the space heating circuit.The store must have a capacity of at least 70
litres and the feed to the space heating circuit must be taken directly from
the store.The appliance has the capability to vary the fuel burning rate
whilst maintaining continuous burner firing.
B1.15 Low temperature boiler
A non-condensing boiler designed as a low temperature boiler and tested
as a low temperature boiler as prescribed by the Boiler Efficiency Directive
(i.e.; the part load test was carried out at average boiler temperature of
40°C).
B1.16 Keep-hot facility
A facility within an instantaneous combination boiler whereby water within
the boiler may be kept hot while there is no demand.The water is kept hot
either (i) solely by burning fuel, or (ii) by electricity, or (iii) both by burning
fuel and by electricity, though not necessarily simultaneously.
Appendix D - Definitions of heating controls
The list of definitions has been discussed and agreed with industry representatives, and, for completeness, includes some controls for
heating systems other than oil central heating.
Automatic bypass valve
A valve to control water flow, operated by the water pressure across it. It
is commonly used to maintain a minimum flow rate through a boiler and to
limit circulation pressure when alternative water paths are closed
(particularly in systems with TRVs).
Boiler anti-cycling device
A device to introduce a time delay between boiler firing. Any energy saving
is due to a reduction in performance of the heating system.The device
does not provide boiler interlock.
Boiler auto ignition
An electrically controlled device to ignite the boiler at the start of each
firing, avoiding use of a permanent pilot flame.
Boiler energy manager
No agreed definition, but typically a device intended to improve boiler
control using a selection of features such as weather compensation, load
compensation, optimum start control, night setback, frost protection,
anticycling control and hot water override.
Boiler interlock
This is not a physical device but an arrangement of the system controls so
as to ensure that the boiler does not fire when there is no demand for
heat. In a system with a combi boiler it can be achieved by fitting a room
thermostat. In a system with a regular boiler it can be achieved by correct
wiring interconnections between the room thermostat, cylinder thermostat,
and motorised valve(s). It may also be achieved by a suitable boiler energy
manager.
Boiler modulator (air temperature)
A device, or feature within a device, to vary the fuel burning rate of a boiler
according to measured room temperature.The boiler under control must
have modulating capability and a suitable interface for connection.
Boiler modulator (water temperature)
A device, or feature within a device, to vary the fuel burning rate of a boiler
according to measured water temperature. It is often fitted within the
boiler casing.The boiler under control must have modulating capability.
Boiler thermostat
A thermostat within the boiler casing to limit the temperature of water
passing through the boiler by switching off the boiler.The target
temperature may either be fixed or set by the user.
‘CELECT-type’ electric heating control
Integrated central control system for electric storage and panel heaters
that provides programmed space temperatures at different times of the day
for a number of separate heating zones in the dwelling. It minimises the
charge period of the storage heaters according to the external
temperature.
Cylinder thermostat
A sensing device to measure the temperature of the hot water cylinder and
switch on and off the water heating. A single target temperature may be set
by the user.
Delayed start
A device, or feature within a device, to delay the chosen starting time for
space heating according to the temperature measured inside or outside the
building.
Frost thermostat
A device to detect low air temperature and switch on heating to avoid
frost damage, arranged to override other controls.
Load compensator
A device, or feature within a device, which adjusts the temperature of the
water circulating through the heating system according to the temperature
measured inside the building.
Motorised valve
A valve to control water flow, operated electrically. A two-port motorised
valve controls water flow to a single destination. A three-port motorised
valve controls water flow to two destinations (usually for space heating and
hot water), and may be either a diverter valve (only one outlet open at a
time) or a mid-position valve (either one, or both, outlets open at a time).
The valve movement may also open or close switches, which are used to
control the boiler and pump.
Night setback
A feature of a room thermostat that allows a lower temperature to be
maintained outside the period during which the normal room temperature
is required.
On/off-peak hot water controller
A control to switch the electrical supply to the main immersion heater
from the off-peak electricity supply. It may also include a boost function so
that some of the stored water can also be heated using on-peak electricity.
Optimum start
A device, or feature within a device, to adjust the starting time for space
heating according to the temperature measured inside or outside the
building, aiming to heat the building to the required temperature by a
chosen time.
Optimum stop
A device, or feature within a device, to adjust the stop time for space
heating according to the temperature measured inside (and possibly
outside) the building, aiming to prevent the required temperature of the
building being maintained beyond a chosen time.
Pipe thermostat
A switch governed by a sensor measuring pipe temperature, normally used
in conjunction with other controls such as a frost thermostat.
Programmable cylinder thermostat
A combined time switch and cylinder thermostat that allows the user to
set different periods with different target temperatures for stored hot
water, usually in a daily or weekly cycle.
39
Appendix D - Definitions of heating controls
Programmable room thermostat
A combined time switch and room thermostat that allows the user to set
different periods with different target temperatures for space heating,
usually in a daily or weekly cycle.
Programmer
Two switches operated by a clock to control both space heating and hot
water.The user chooses one or more ‘on’ periods, usually in a daily or
weekly cycle. A mini-programmer allows space heating and hot water to be
on together, or hot water alone, but not heating alone. A standard
programmer uses the same time settings for space heating and hot water. A
full programmer allows the time settings for space heating and hot water to
be fully independent.
Pump modulator
A device to reduce pump power when not needed, determined by hydraulic
or temperature conditions or firing status of the boiler.
Pump over-run
A timing device to run the heating system pump for a short period after
the boiler stops firing to discharge very hot water from the boiler heat
exchanger.
Room thermostat
A sensing device to measure the air temperature within the building and
switch on and off the space heating. A single target temperature may be set
by the user.
Self-adaptive (or self-learning) control
A characteristic of a device (of various types) that learns from experience
by monitoring, and modifies its subsequent behaviour accordingly.
Temperature and time zone control (or full zone control)
A control scheme in which it is possible to select different temperatures at
different times in two (or more) different zones.
Time switch
An electrical switch operated by a clock to control either space heating or
hot water, or both together but not independently.The user chooses one
or more ‘on’ periods, usually in a daily or weekly cycle.
Thermostatic radiator valve
A radiator valve with an air temperature sensor, used to control the heat
output from the radiator by adjusting water flow.
Weather compensator
A device, or feature within a device, that adjusts the temperature of the
water circulating through the heating system according to the temperature
measured outside the building.
Zone control
A control scheme in which it is possible to select different times and/or
temperatures in two (or more) different zones.
40
References
References used in CHeSS (year 2005)
[1] The Building Regulations 2000. Approved Document L1, Conservation
of fuel and power in dwellings, 2002 Edition
21 ODPM website www.odpm.gov.uk; see ‘Building Regulations’ then ‘The
Building Act 1984 and building regulations’ then ‘Approved documents’.
[2] Section 6: Energy, of the Domestic Technical Handbook on possible
ways of complying with the Building (Scotland) Regulations 2004. See
website www.sbsa.gov.uk.
22 The Building Regulations 2000. Approved Document L1, Conservation
of fuel and power in dwellings, 2002 Edition
[3] Domestic heating by gas: boiler systems : guidance for installers and
specifiers: Energy Efficiency Best Practice in Housing (CE30)
[4] Domestic heating by oil: boiler systems : guidance for installers and
specifiers: Energy Efficiency Best Practice in Housing (CE29)
[5] Domestic Heating Design Guide, CIBSE, May 2003
[6] The Government’s Standard Assessment Procedure for Energy Rating
of Dwellings, 2001 Edition
[7] BS 1566: 2002, Copper indirect cylinders for domestic purposes
[8] BS 7206: 1990, Specification for unvented hot water storage units and
packages
[9] Waterheater Manufacturers’ Association Performance Specification for
Thermal Stores, 1999
[10] Benchmark Code of Practice for the Installation, Commissioning and
Servicing of Central Heating Systems (available from Heating &
Hotwater Information Council, website www.centralheating.co.uk or
telephone 0845 600 2200)
23 Section 6: Energy, of the Domestic Technical Handbook on possible
ways of complying with Building (Scotland) Regulations 2004 (see
website www.sbsa.gov.uk)
24 The Building Regulations (Northern Ireland) 2000.Technical Booklet F:
Conservation of fuel and power (December 1998 edition) (accessible
on website www.dfpni gov.uk)
25 Boiler Efficiency Database: see website www.boilers.org.uk.
26 The Government’s Standard Assessment Procedure for Energy Rating
of Dwellings, 2001 Edition
27 BS 1566:2002, Copper indirect cylinders for domestic purposes
28 BS 3198:1981, Specification for copper hot water storage combination
units for domestic purposes
29 BS 7206:1990, Specification for unvented hot water storage units and
packages
30 Waterheater Manufacturers’ Association Performance Specification for
Thermal Stores, 1999.
[11] The Building Regulations (Northern Ireland) 2000.Technical booklet F,
Conservation of fuel and power (December 1998). See website
www2.dfpni.gov.uk/buildingregulations/.
31 Benchmark Code of Practice for the Installation, Commissioning and
Servicing of Central Heating Systems (available from Heating &
Hotwater Information Council, website www.centralheating.co.uk or
telephone 0845 600 2200)
[12] BS 5449: 1990 incorporating Amendment No.1 issued March 2002,
Specification for forced circulation hot water central heating systems
for domestic premises
32 BS 5410-1:21997, Code of Practice for oil firing - Part 1. Installations up
to 45kW output capacity for space heating and hot water supply
purposes
[13] BS 7671: 2001, Requirements for electrical installations, IEE Wiring
Regulations, Sixteenth edition
33 General Information Leaflet 83, ‘Domestic boiler anti-cycling controls an evaluation’, London, 1997
[14] BS 7593: 1992, Code of Practice for Treatment of water in domestic hot
water central heating systems
34 BREDEM-12, Building Research Establishment Report BR315. BRE,
Garston, 1996
[15] European Standard (Telecommunications series) ETSI EN 300 220-1
v1.3.1 (2000-09): Electromagnetic compatibility and Radio spectrum
Matters (ERM); Short Range Devices (SRD); Radio equipment to be
used in the 25 MHz to 1000 MHz frequency range with power levels
ranging up to 500 mW;Part 1:Technical characteristics and test
methods
35 BRE Report BR354 : Domestic Energy Fact File 1998, L D Shorrock and
G A Walters
36 BS 5449:1990 incorporating Amendment No. 1 issued March 2002,
Specification for forced circulation hot water central heating systems
for domestic premises
37 BS 7593:1992, Code of Practice for Treatment of water in domestic hot
water central heating systems
References used elsewhere in this Guide
17 The Boiler (Efficiency) Regulations 1993, SI (1993) No 3083, as amended
by the Boiler (Efficiency) (Amendment) Regulations 1994, SI (1994) No
3083.
38 HHIC Guidance Notes for the installation of domestic gas high
efficiency (condensing) boiler, HHIC, September 2002
39 Technical Information Book 4, OFTEC
40 Technical Information Book 3, OFTEC
18 Central Heating System Specifications
(CHeSS) - Year 2005 (GIL 59)
41 Aspects of the risk of environmental damage caused by spillage from oil
storage tanks, OFTEC Ref TI/133
19 Domestic Heating Design Guide, CIBSE, May 2003
42 The Building Regulations 2000. Approved Document J, Combustion
Appliances & Fuel Storage Systems
20 Council Directive 92/42/EEC on efficiency requirements for new
hotwater boilers fired with liquid or gaseous fuels. Official Journal of
the European Communities No L/167/17. 21 May 1992, p. 92.
43 Statutory Instrument 2001 No. 2954.The control of Pollution (Oil
Storage) (England) Regulations 2001
41
References
44 Fire Protection of Oil Storage Installations for Classes 2 and 3, OFTEC
Ref TI/136
45 Installing Oil Supply Pipes Underground, OFTEC Ref TI/134
46 Installation of Top Outlet Fuel Storage Tanks and Suction Oil Supply
Pipe Sizing, OFTEC Ref TI/139
47 Technical Information Book 2, OFTEC
48 Statutory Instrument 1991 No. 1156 (S. 43) The Control of Pollution
(Continuation of Byelaws) (Scotland) Order 1991
49 Section 3: Environment, of the Domestic Technical handbook on
possible ways of complying with building (Scotland) Regulations 2004
(see website www.sbsa.gov.uk)
50 Solar hot water installation guide: Energy Efficiency Best Practice
Programme in Housing CE131 [to be published autumn 2005]
42
Energy Efficiency Best Practice in Housing
CE29
Domestic heating by oil: boiler systems
This publication (including any drawings forming part of it) is intended for general guidance
only and not as a substitute for the application of professional expertise. Anyone using this
publication (including any drawings forming part of it) must make their own assessment of
the suitability of its content (whether for their own purposes of those of any client or
customer), and the Energy Saving Trust (EST) cannot accept responsibility for any loss, damage
or other liability resulting from such use.
Energy Efficiency Best Practice in Housing
Helpline: 0845 120 7799
Fax: 0845 120 7789
Email: [email protected]
Web: www.est.org.uk/bestpractice
Energy Efficiency Best Practice in Housing is managed by
the Energy Saving Trust on behalf of the Government.
CE29 © Energy Saving Trust. February 2005. E&OE.
All technical information was produced by the Building Research Establishment (BRE) on behalf of the EST.
Printed on Revive Silk which contains 75% de-inked post consumer waste and a maximum of 25% mill broke.
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement