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9
Provide two (2) permanent openings, one (1) located within 12 inches of the
floor and one (1) within 12 inches of the ceiling, or roof, of the room. These
openings shall allow for direct exchange of air between the room and
outdoors. If required, ducting between the room and the outdoors shall be
provided.
• For horizontally -oriented ducts, each opening shall have a minimum free
area of one (1) square inch per 2000 BTUH of the total input rate (sum of
the individual appliance input rates) of all appliances to be installed in the
room.
• For vertically -oriented ducts, the minimum free area may be reduced to
one (1) square inch per 4000 BTUH of the total input rate (sum of the
individual appliance input rates) of all appliances to be installed in the
room.
• The minimum dimension of any air opening shall not be less than 3-
inches.
• When an opening in the outside wall must be provided, it should be
furnished with properly screened metal sleeves.
2. Full Basement (example of an unconfined space)
a. Where a furnace is installed in a full basement, in a building of conventional
construction with normal air infiltration, infiltration is normally adequate to
provide air for combustion and ventilation.
b. In buildings of unusually tight construction (such as those where weather
stripping and storm sash windows are used, and where basement windows
are also weather-stripped), one (1) permanent opening connecting to a well-
ventilated attic, or with the outdoors shall be provided, using a duct, if
necessary. This opening shall have a minimum free area of one (1) square
inch per 5000 BTUH of total input rate (sum of the individual appliance input
rates) of all appliances to be installed in the basement.
When an opening in the outside wall must be provided, it should be furnished
with properly screened metal sleeves.
If an exhaust fan, additional air consuming machines (e.g. an air compressor), or a
return air grill is present in the furnace room, there should be increased concern about
providing adequate airflow to the furnace. Additional efforts may be required to assure
an adequate supply of combustion and ventilation air is available to the furnace under
all conditions.