Page 12
Installer’s Information Manual
Exposure to the following substances in the combustion air
supply may also require outdoor air for combustion:
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Aerosols
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Permanent wave solutions
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Chlorinated waxes, bleaches a nd cleaners
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Cat litter
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Chlorine-based swimming pool chemicals
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Cleaning solvents
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Paint removers and varnishes
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Adhesives
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Anti-static fabric softeners
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Most refrigerants
WARNING
: Combustion air that contains chlorine,
fluorine, bromine or iodine could cause corrosion in heat
exchanger and may result in nausea or death by
asphyxiation.
UNCONFINED SPACE INSTALLATION (non-direct
vent)
The National Fuel Gas Code, ANSI Z223.1/NFPA 54 and
CAN/CGA B149 Installation Codes do not require that you
m ake special provisions for combustion and ventilation air
when furnace is in an "unconfined space" and building is
not of "unusually tight construction."
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"Unconfined spaces" have a volume of at least 50
cubic feet per 1000 Btu per hour combined input rating
of all appliances installed in the space. For example: a
100,000 Btu/hr furnace and a 40,000 Btu/hr water
heater would require a volume of at least 140,000 X 50
÷ 1,000 or 7,000 cubic feet.
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"Unusually tight construction" means windows and
doors are either tight fitting or are sealed construction
and that walls are covered with a continuous, sealed
vapor barrier and drywall or similar materials having
sealed joints.
If you meet the volume requirements for unconfined space,
the building is not of unusually tight construction and there
are no airborne contaminants, as listed above, you may
install this fu rnace without making special provisions for
combustion and ventilation air. Otherwise, follow the
instructions for "confined space installation" below or direct
vent the furnace using two pipes.
CONFINED SPACE INSTALLATION (non-direct
vent)
A non-direct vented furnace installed in a confined space
must take combustion and ventilation air from an
unconfined space within the building or from outdoors.
However, if the building is of unusually tight construction all
combustion air must come from outdoors. Also, if retu rn air
is taken directly from a hallway or space next to fu rnace
that communicates with fu rnace spaces, all combustion air
must come from outdoors .
WARNING
: You must provide permanent air
openings to a confined fu rnace installation space from
another area as described below. Failure to do so could
cause inadequate combustion and ventilation air and may
result in nausea or death by asphyxiation.
ALL COMBUSTION AND VENTILATION AIR FROM
INSIDE THE BUILDING
The confined furnace space must be provided with two
permanent openings to an additional room of sufficient
volume so that the combined volumes of the spaces meet
the criteria above for an unconfined space not of unusually
tight construction. The total input of all gas appliances
within the combined space must be considered in making
this determination.
Each opening must have minimum free area of one square
inch per 1,000 Btu per hour of the total combined input
rating of all gas appliances within the confined fu rnace
space, but not less than 100 square inches. One opening
must be within 12 inches of the top and one opening within
12 inches of the bottom of the fu rnace space. Th e shortest
side of each air opening must be at least 3 inches long.
See Figure 9.
For example:
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A 90,000 Btu/hr furnace and a 40,000 Btu/hr water
heater would require free area openings of 130,000 ÷
1,000 or 130 square inches.
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A 54,000 Btu/hr furnace and a 40,000 Btu/hr water
heater would require the minimum free area openings
of 100 square inches.
Figure 9. Confined Space, All Air From Inside The Building.
ALL COMBUSTION AND VENTILATION AIR FROM
OUTDOORS
The furnace space must be provided with two permanent
air openings communicating directly, or by ducts, with the
outdoors or spaces that freely access the outdoors. Well-
ventilated attics or crawl spaces usually satisfy this
requirement. These openings will give fu rnace free access
to fresh air for combustion and ventilation.
