The wrong way to save money on HVAC

The wrong way to
save money on HVAC
By Bill Dove, CM,
HVAC trainer and installation specialist
Application Note
How to advise your clients against
potentially harmful decisions
When most homeowners think about reducing their
heating costs without additional expenditures, they
tend to think in terms of temperature. They want more
heat for the same money, they look for “free” heat,
they seal sources of cold drafts, and other, sometimes
very ingenious, solutions. They forget to think about
oxygen, carbon dioxide, carbon monoxide, indoor air
contaminants, what they are breathing and where it
came from (or didn’t come from), and the overall cause
and effect of their actions.
“Let’s close the registers in
unoccupied rooms”
This reduces air volume through
the furnace, elevates heat
exchanger temperatures, reduces
heat transfer into the home,
elevates vent temperatures and
increases heat losses up the
chimney, causes furnace short
cycling and shortens component
life. There is no savings here,
only additional losses and costs.
Better to add a zoning system,
or use the lowest fan speed for
continuous fan operation to keep
the temperature more evenly
distributed. This may allow for
one or two degree reduction in
the thermostat setting. For older
furnaces, a relay may be needed
to operate low speed on a “G”
demand, but bring on high speed
for a “Y” demand.
“Let’s shut off some
Now we’re looking at some possible broken pipes, boiler short
cycling, more frequent hot surface igniter failures, and possible
increased maintenance schedules. Again we can add some
zoning for more effective temperature control. An old trick with
cast iron radiation and large
water content boilers was to
use two stage heat thermostats.
Stage one started the circulator,
stage two started the burner.
This was particularly effective
with zoned systems.
Electric oven? How much does
electricity cost at a COP (coefficient of performance, or the ratio
of the change in heat to the supplied work) of one? How much
does an appliance serviceman
charge to replace an oven heating element?
OK, but don’t forget to open
the windows. Un-vented space
heaters use oxygen and replace
room air with CO2, CO and water
vapor. CO2 is heavier than air
and will settle at the heater
where there should be oxygen,
CO is lighter than air and will
rise to the ceiling. Excess humidity will damage the structure.
If the CO2 don’t get you from
below, the CO will get you
from above.
Lint. Extremely flammable lint!
Lint you shouldn’t breath. Lint
that will clog the furnace filter (until it bypasses the filter
and coats the coils). Chemicals.
Anti-static chemicals that will
coat the furnace flame sensor with electrically insulating
compounds that will eventually
cause a no-heat call. How much
does it cost to clean a flame sensor? Is it a gas drier? Then we’re
back to the same objections as a
space heater or gas oven.
“Why should we let all that
“Let’s buy a kerosene space hot air from the clothes
heater and take it from
drier vent outdoors instead
room to room with us.”
of indoors?”
“Let’s use the oven to heat
the kitchen”
Gas oven? Its effects are the
same as a kerosene heater, but
faster and worse. Bad, bad, bad.
From the Fluke Digital Library @
“I stopped up those
pipes to the outdoors
in my furnace room”
Serious health hazard. Furnaces,
boilers, water heaters, gas driers need a constant supply of
fresh air. Vent systems need a
constant supply of ventilation air.
There are codes to comply with,
and there are also the laws of
physics to work with. What if we
connected that combustion air
supply to the return and added a
small supply register in the supply trunk in the equipment room
and latched on the lowest fan
speed for continuous fan operation? We just provided a continuous means of whole house
ventilation air at a house positive
pressure with a continuous (preheated during the heat cycle)
air supply to the furnace room.
And don’t forget the balancing
damper (locked in place) in the
outdoor air supply duct. This
would satisfy NFGC ANSI Z223.15.3.4 “Specially Engineered
Systems”. (Allow a liberal 50 cfm
for combustion air supply and
venting in the equipment room
for every 100,000 Btus input.)
“I cut a hole in the return
here next to my basement
wood stove”
Warning: you could die. Think
about this. Let’s create a negative pressure in the equipment
area, ruin our venting, and suck
lots of CO from the wood stove
into the rest of the house. Yes, it
has happened!
“I use my fireplace to heat
the family room”
And that old fireplace just sucks
the heat out of the house right
up that big ole masonry chimney
so the furnace runs longer. Then
when it’s bedtime and there
are still glowing embers in the
fireplace and we lose draft, the
house can suddenly breath again
and suck make-up air down the
chimney, right across that bed
of glowing embers. That bed
of embers that produces phenomenal amounts of CO. Serious
health hazard. Fireplace inserts
and free-standing stoves that
are sealed from the living space
and get all of their combustion
air from outdoors are OK. Sell
them one.
“Can I capture the heat from
my furnace vent?”
No. Lowered vent temperatures
increase wet time and increase
the likelihood of vent damage.
There have been devices on the
market that sink the heat from
vent connectors by conduction/
radiation or conduction/convection. Application of these devices
with older furnaces with high
vent temperatures may not have
been as detrimental as applying these devices to a modern
furnace with reduced vent temperatures. In either case, these
devices are no longer recommended.
Be prepared for some off-thewall energy saving questions,
and consider the total cascading
effect before answering. Be careful out there.
Bill Dove has worked in the HVAC trades
since 1977 as a serviceman, supervisor,
instructor, and consultant
Fluke. Keeping your world
up and running.®
Fluke Corporation
PO Box 9090, Everett, WA 98206 U.S.A.
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©2008 Fluke Corporation.
Specifications subject to change without notice.
Printed in U.S.A. 11/2008 3399487 A-EN-N Rev A
Modification of this document is not permitted
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