5
installed in the combined space shall be considered in making
this determination. Each opening shall have a minimum free
area of 1 square inch per 1,000 BTU per hour of the total input
rating of all gas utilization equipment in the confined space, but
not less than 100 square inches. One opening shall be within 12
inches of the top and one within 12 inches of the bottom of the
enclosure (Figure 1 ).
Furnace
Water
Heater
Opening
Chimney or Gas Vent
Opening
NOTE: Each opening must have
a free area of not less than one
square inch per 1000 BTU of
the total input rating of all equip-
ment in the enclosure, but not
less than 100 square inches.
Figure 1
Equipment Located in Confined Spaces; All
Air from Inside Building. See 5.3.3-a
.
(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 (Figure 2).
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)
Figure 2
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 (Figure 3).
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)
Figure 3
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 (Figure 4).
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.
Figure 4
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.
