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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.
Table 1
Combined input of all
appliances in
confined space
BTU/hr(kW)
75,000(23)
100,000(30)
125,000(37)
150,000(45)
175,000(53)
200,000(60)
225,000(68)
250,000(75)
275,000(83)
300,000(90)
325,000(98)
350,000(105)
375,000(113)
400,000(120)
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.
8
Acceptable Equivalent duct
Required
diameter
free area of
duct
A
B
1
2
2
2
in(mm)
in(mm)
in
(mm
)
11(7,000)
4(100)
5(125)
14(9,000)
4(100)
5(125)
18(12,000)
5(125)
6(150)
22(14,000)
5(125)
6(150)
25(16,000)
6(150)
7(175)
29(19,000)
6(150)
7(175)
32(21,000)
6(150)
7(175)
36(23,000)
7(175)
8(200)
40(26,000)
7(175)
8(200)
43(28,000)
7(175)
8(200)
47(30,000)
8(200)
9(225)
50(32,000)
8(200)
9(225)
54(35,000)
8(200)
9(225)
58(37,000)
9(225)
10(250)
.
Figure: 2 Equipment Location
and Combustion/Ventilation Air
Requirements
(a)
Permanent
Ventilation
Combustion
Air Duct
(b)
(c)
Outlet Air
(d)
*U.S. installations require a dual duct system.
12" Grade
Air
12"
Venting
Outdoor
Air Ducts
Combustion
Inlet
Air Ducts
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