507324-01B
Page 5 of 32
Issue 1809
also be located close to the chimney or vent termination
point.
•
Do not install the furnace where drafts might blow
directly into it. This could cause improper combustion.
•
Do not block the furnace combustion air openings with
clothing, boxes, doors, etc. Air is needed for proper
combustion and safe unit operation.
•
When the furnace is installed in an attic or other
insulated space, keep insulation away from the
furnace.
NOTE:
The Commonwealth of Massachusetts stipulates
these additional requirements:
•
Gas furnaces shall be installed by a licensed plumber
or fitter only.
•
The gas cock must be “T handle” type.
•
When a furnace is installed in an attic, the passageway
to and service area surrounding the equipment shall
be floored.
Combustion, Dilution & Ventilation Air
In the past, there was no problem in bringing in sufficient
outdoor air for combustion. Infiltration provided all the air
that was needed. In today’s homes, tight construction
practices make it necessary to bring in air from outside
for combustion. Take into account that exhaust fans,
appliance vents, chimneys, and fireplaces force additional
air that could be used for combustion out of the house.
Unless outside air is brought into the house for combustion,
negative pressure (outside pressure is greater than inside
pressure) will build to the point that a downdraft can occur
in the furnace vent pipe or chimney. As a result, combustion
gases enter the living space creating a potentially
dangerous situation.
In the absence of local codes concerning air for combustion
and ventilation, use the guidelines and procedures in this
section to install these furnaces to ensure efficient and
safe operation. You must consider combustion air needs
and requirements for exhaust vents and gas piping.
A portion of this information has been reprinted
with permission from the National Fuel Gas Code
(ANSI-Z223.1). This reprinted material is not the complete
and official position of the ANSI on the referenced subject,
which is represented only by the standard in its entirety.
All gas fired appliances require air for the combustion
process. If sufficient combustion air is not available, the
furnace or other appliances will operate inefficiently
and unsafely. Enough air must be provided to meet the
needs of all fuel burning appliances and appliances such
as exhaust fans which force air out of the house. When
fireplaces, exhaust fans, or clothes dryers are used at the
same time as the furnace, much more air is necessary to
ensure proper combustion and to prevent a downdraft.
Insufficient air causes incomplete combustion which can
result in carbon monoxide.
In addition to providing combustion air, fresh outdoor air
dilutes contaminants in the indoor air. These contaminants
may include bleaches, adhesives, detergents, solvents
and other contaminants which can corrode furnace
components.
The requirements for providing air for combustion and
ventilation depend largely on whether the furnace is
installed in an unconfined or a confined space.
Insufficient combustion air can cause headaches,
nausea, dizziness or asphyxiation. It will also cause
excess water in the heat exchanger resulting in rusting
and premature heat exchanger failure. Excessive
exposure to contaminated combustion air will result
in safety and performance related problems. Avoid
exposure to the following substances in the combustion
air supply:
•
Permanent wave solutions
•
Chlorinated waxes and cleaners
•
Chlorine base swimming pool chemicals
•
Water softening chemicals
•
De-icing salts or chemicals
•
Carbon tetrachloride
•
Halogen type refrigerants
•
Cleaning solvents (such as perchloroethylene)
•
Printing inks, paint removers, varnishes, etc.
•
Hydrochloric acid
•
Antistatic fabric softeners for clothes dryers
•
Masonry acid washing materials
WARNING
Unconfined Space
An unconfined space is an area such as a basement
or large equipment room with a volume greater than 50
cubic feet (1.42 m3) per 1,000 Btu (.29 kW) per hour of
the combined input rating of all appliances installed in that
space. This space also includes adjacent rooms which are
not separated by a door. Though an area may appear to
be unconfined, it might be necessary to bring in outdoor air
for combustion if the structure does not provide enough air
by infiltration. If the furnace is located in a building of tight
construction with weather stripping and caulking around
the windows and doors, follow the procedures in the air
from outside section.
