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Figure: 2 Equipment Location
and Combustion/Ventilation Air
Requirements
Combustion
Air Duct
Permanent
Ventilation
Air
12” Grade
12”
Outdoor
Air Ducts
Venting
Combustion
Inlet
Air Ducts
Outlet Air
(a)
(b)
(d)
(c)
8
Air Opening Requirements
(a) EQUIPMENT LOCATED IN CONFINED SPACES; ALL AIR FROM
INSIDE THE BUILDING.
Two permanent openings (top and bottom) 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 (22 cm²/kW) input of all appliances in the confined space, but
not less than 100 square inches (645 cm²).
b) BASEMENT INSTALLATION, EQUIPMENT LOCATED IN CON-
FINED SPACES; ALL AIR FROM OUTDOORS.
Outside air inlets shall be a minimum of 12” (300mm) above the grade
(snow) line. When supplying air directly from the outdoors:
For American installations: Two openings (top and bottom) shall be
provided with each opening having 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.
For Canadian installations: Canadian codes specify single air supply
source. Canadian customers and authorities having jurisdiction may use
the sizing listed in Table 1. When using a single air supply, the duct shall
terminate within 1 foot (300 mm) above and within 2 feet (600 mm) hori-
zontally from the burner level of the appliance having the largest input.
Notes:
1.Maximum lenght of ducts in column A is 20 equivalent feet(6.1 meters).
2.Maximum lenght of ducts in column B is 50 equivalent feet(15.2 meters).
(c) EQUIPMENT LOCATED IN CONFINED SPACES; ALL AIR FROM
OUTDOORS.
For American installations: When supplying air directly from the out-
doors using horizontal ducting, each opening shall have a free minimum
area of one square inch per 2,000 BTU/hour (11 cm²/kW) of total input
rating of all appliances in the confined space.
For Canadian installations: Refer to Table 1 of part (b).
(d) EQUIPMENT LOCATED IN CONFINED SPACES; ALL AIR FROM
OUTDOORS THROUGH VENTILATED ATTIC
.
For American installations: 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 appli-
ances in the confined space.
*U.S. installations require a dual duct system.
A
1
B
2
BTU/hr(kW)
in
2
(mm
2
)
in(mm) in(mm)
75,000(23) 11(7,000) 4(100) 5(125)
100,000(30) 14(9,000) 4(100) 5(125)
125,000(37) 18(12,000) 5(125) 6(150)
150,000(45) 22(14,000) 5(125) 6(150)
175,000(53) 25(16,000) 6(150) 7(175)
200,000(60) 29(19,000) 6(150) 7(175)
225,000(68) 32(21,000) 6(150) 7(175)
250,000(75) 36(23,000) 7(175) 8(200)
275,000(83) 40(26,000) 7(175) 8(200)
300,000(90) 43(28,000) 7(175) 8(200)
325,000(98) 47(30,000) 8(200) 9(225)
350,000(105) 50(32,000) 8(200) 9(225)
375,000(113) 54(35,000) 8(200) 9(225)
400,000(120) 58(37,000) 9(225) 10(250)
Acceptable Equivalent duct
diameter
Combined input of all
appliances in
confined space
Required
free area of
duct
Table 1
Index