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IO-247A 12/04
(b) All Air from Outdoors: The confined space shall be provided
with two permanent openings, one commencing within 12
inches of the top and one commencing within 12 inches of
the bottom of the enclosure. The openings shall
communicate directly, or by ducts, with the outdoors or
spaces (crawl or attic) that freely communicate with the
outdoors.
1. When directly communicating with the outdoors, each
opening shall have a minimum free area of 1 square inch
per 4,000 BTU per hour of total input rating of all
equipment in the enclosure.
Furnace
Water
Heater
Outlet Air
Chimney or Gas Vent
NOTE: The inlet and outlet air
openings must each have a free
area of not less than one square
inch per 4000 BTU of the
total input rating of all equipment
in the enclosure.
Inlet Air
Ventilation louvers for
unheated crawl space
Alternate
air inlet
Ventilation louvers
(each end of attic)
Equipment Located in Confined Spaces; All Air from Outdoors—Inlet
Air from Ventilated Crawl Space and Outlet Air to Ventilated Attic.
See 5.3.3-b
2. When communicating with the outdoors through vertical
ducts, each opening shall have a minimum free area of
1 square inch per 4,000 BTU per hour of total input rating
of all equipment in the enclosure.
Furnace
Water
Heater
Outlet Air
Chimney or Gas Vent
NOTE: The inlet and outlet air
openings must each have a free
area of not less than one square
inch per 4000 BTU of the
total input rating of all equipment
in the enclosure.
Inlet air duct
[ends 1 ft (300 mm)
above floor]
Ventilation louvers
(each end of attic)
Equipment Located in Confined Spaces; All Air from Outdoors
Through Ventilated Attic. See 5.3.3-b.
3. When communicating with the outdoors through horizontal
ducts, each opening shall have a minimum free area of
1 square inch per 2,000 BTU per hour of total input rating
of all equipment in the enclosure.
Furnace
Water
Heater
Chimney or Gas Vent
NOTE: The air duct openings
must have a free area of not
less than one square inch per
2000 BTU of the total input
rating of all equipment in the
enclosure*.
Outlet air duct
Inlet air duct
*If the appliance room is located against an outside wall and the
air openings communicate directly with the outdoors, each opening
shall have a free area of not less than one square inch per 4,000
BTU per hour of the total input rating of all appliances in the
enclosure.
Equipment Located in Confined Spaces;
All Air from Outdoors. See 5.3.3-b.
4. When ducts are used, they shall be of the same cross-
sectional area as the free area of the openings to which
they connect. The minimum dimension of rectangular air
ducts shall not be less than 3 inches.
Furnace
Water
Heater
Opening
Chimney or Gas Vent
NOTE: The single opening must have
a free area of not less than one
square inch per 3000 BTU of
the total input rating of all equip-
ment in the enclosure, but not less than
the sum of the areas of all vent
connectors in the confined space.
Alternate
Opening
Location
Equipment Located in Confined Spaces; All Air from Outdoors -
Single Air Opening. See 5.3.3-b.
5. One permanent opening may be permitted, provided the
equipment has clearances of at least 1” from the sides
and back and 6” from the front. The opening shall
communicate directly with the outdoors and must be
located within 12” of the top of the enclosure. The
minimum free area of the opening shall be 1 square inch
per 3,000 BTU per hour of total input rating of all
equipment in the enclosure. The minimum free area shall
not be less than the sum of the areas of all vent
connectors in the confined space.
5.3.4 Specially Engineered Installations:
The requirements of 5.3.3 shall not necessarily govern when
special engineering, approved by the authority having
jurisdiction, provides an adequate supply of air for combustion,
ventilation, and dilution of flue gases.