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Commercial HVAC Maintenance in Virginia
Beach, VA
Maintaining Proper Ventilation for Combustion
Systems
Anytime you maintain, retrofit, or replace a gas heating system
you also need to be concerned with air quality. Combustion air
is needed by all oil and gas heating systems to support the combustion
process. This air is provided in some homes by unintentional air
leaks, or by air ducts that connect to the outdoors. The combustion
process creates several byproducts that are potentially hazardous
to human health and can cause deterioration in your home. You
can protect yourself from these hazards, as well as maintain energy
efficiency, by ensuring that your chimney system functions properly
and that your gas heating system is properly ventilated. In some
cases, installing a sealed-combustion furnace or boiler can also
help.
Chimneys
Properly functioning chimney systems will carry combustion byproducts
out of the home. Therefore, chimney problems put you at risk of
having these byproducts, such as carbon monoxide, spill into your
home.
Most older gas furnaces and boilers have naturally drafting chimneys.
The combustion gases exit the home through the chimney using only
their buoyancy combined with the chimney's height. Naturally drafting
chimneys often have problems exhausting the combustion gases because
of chimney blockage, wind or pressures inside the home that overcome
the buoyancy of the gases.
Atmospheric, open-combustion furnaces and boilers, as well as
fan-assisted furnaces and boilers, should be vented into masonry
chimneys, metal double-wall chimneys, or another type of manufactured
chimney. Masonry chimneys should have a fireclay, masonry liner
or a retrofitted metal flue liner.
Many older chimneys have deteriorated liners or no liners at all
and must be relined during furnace or boiler replacement. A chimney
should be relined when any of the following changes are made to
the combustion heating system:
•
When you replace an older furnace or boiler with a newer one that
has an AFUE of 80% or more. These mid-efficiency appliances have
a greater risk of depositing acidic condensation droplets in chimneys,
and the chimneys must be prepared to handle this corrosive threat.
The new chimney liner should be sized to accommodate both the
new heating appliance and the combustion water heater by the installer.
•
When you replace an older furnace or boiler with a new 90+ AFUE
appliance or a heat pump. In this case, the heating appliance
will no longer vent into the old chimney, and the combustion water
heater will now vent through an oversized chimney. This oversized
chimney can lead to condensation and inadequate draft. The new
chimney liner should be sized for the water heater alone, or the
water heater in some cases can be vented directly through the
wall.
Other Ventilation Concerns
Some fan-assisted, non-condensing furnaces and boilers, installed
between 1987 and 1993, may be vented horizontally through high-temperature
plastic vent pipe (not PVC pipe, which is safely used in condensing
furnaces). This type of venting has been recalled and should be
replaced by stainless steel vent pipe. If horizontal venting was
used, an additional draft-inducing fan may be needed near the
vent outlet to create adequate draft. Floor furnaces may have
special venting problems because their vent connector exits the
furnace close to the floor and may travel 10 to 30 feet before
reaching a chimney. Check to see if this type of venting or the
floor furnace itself needs replacement. If you smell gases, you
have a venting problem that could affect your health.
Contact
your local utility or heating contractor to have this venting
problem repaired immediately.
US Department of Energy
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 Commercial
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Commercial & Residential Service Provider
in Virginia Beach, VA
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