Confined Space Air Requirements for
U.S. Installations
Refer to Figure 6 (a), (b), (c) or (d) for proper sizing and
location of combustion air ducts and openings.
CHECK
LOCAL CODES.
(a) Equipment located in confined spaces; all air from
inside the building.
Two permanent openings shall be provided connecting
the confined space (e.g., closet, small room) with the
unconfined space. Each opening shall have a free area
of one square inch per 1,000 BTU/hour input (22
cm²/kW) of all appliances in the confined space, but not
less than 100 square inches (645 cm²). The top open-
ing shall commence within 300mm (12 in.) of the top of
space and the bottom opening shall commence within
300mm (12 in.) of the bottom of the enclosure.
(b) Basement installation, equipment located in con-
fined spaces; all air from outdoors.
When supplying air directly from the outdoors, each
opening shall have a minimum free area of one square
inch per 4,000 BTU/hour input (5.5 cm²/kW) of total
input rating of all appliances in the confined space. The
inlets shall be a minimum of 300mm (12 in.) above the
grade (snow) line. The top opening shall commence
within 300mm (12 in.) of the top of the confined space.
(c) Equipment located in confined spaces; all air from
outdoors.
When supplying air directly from the outdoors using hor-
izontal ducting, each opening shall have a free mini-
mum area of one square inch per 2,000 BTU/hour (11
cm²/kW) of total input rating of all appliances in the con-
fined space.
(d) Equipment located in confined spaces; all air from
outdoors through ventilated attic.
When supplying air directly through vertical ducting,
each opening shall have a free minimum area of one
square inch per 4,000 BTU/hour (5.5 cm²/kW) of total
input rating of all appliances in the confined space.
CONFINED
SPACE
PERMANENT
OPENINGS
EQUIPMENT LOCATED IN CONFINED SPACES;
ALL AIR FROM INSIDE THE BUILDING.
(a)
UNCONFINED
SPACE
CONFINED
SPACE
ATTIC LOUVERS TO OUTDOORS
EQUIPMENT LOCATED IN CONFINED SPACES; ALL AIR
FROM OUTDOORS THROUGH VENTILATED ATTIC.
(d)
INLET AIR
DUCT
OUTLET
AIR
BASEMENT INSTALLATION, EQUIPMENT LOCATED
IN CONFINED SPACES; ALL AIR FROM OUTDOORS
(b)
CONFINED
SPACE
GRADE
300mm
(12 in.)
300mm
(12 in.)
Figure 6
Combustion Air Supply Openings And Ducts
(U.S.A.)
COMBUSTION
AIR DUCT
PERMANENT
VENTILATION
AIR.
300mm
(12 in.)
ABOVE
GRADE
OR
SNOW
LINE
EQUIPMENT LOCATED IN CONFINED
SPACES; ALL AIR FROM OUTDOORS.
(c)
CONFINED
SPACE
COMBUSTION
300mm (12 in.)
300mm (12 in.)
300mm (12 in.)
OUTDOORS
AIR DUCT
VENTILATION
REVERSE
FLOW OF
GASES
EXHAUST
FAN
Figure 7
Air Moving Devices
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