For buildings that are not well sealed (do not have tight fitting doors and windows) natural air infiltration may provide sufficient air required for combustion and ventilation. For buildings using tight construction (newer and renovated structures), the air supply shall be introduced from the outdoors, regardless of whether the space is confined or unconfined.
Combustion Air “Supply” Ducts
Air supply ducts shall be of galvanized steel or equivalent corrosion resistant material. A single air duct may not be substituted when required for upper and lower air openings. Horizontal upper combustion air ducts shall not slope downward toward the air inlet.
Louvers and Grills
Openings for air supply ducts must provide free unobstructed air movement. Louver and grill openings must be sized to ensure that the FREE OPEN AREA is never less than the area of the air duct.
LOCATION:
The location for top and bottom openings are as follows;
For American installations:The top opening shall commence within 12” (30 cm) of the top of space and the bottom opening shall commence within 12” (30 cm) of the bottom of the enclosure.
For Canadian installations:The top opening shall be located as close to the ceiling as practical but never lower than the relief opening of the lowest draft control device. The bottom opening shall be located neither more than 18 inches (450 mm), nor less than 6 inches (150 mm), above floor level.
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 |
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confined space (e.g., closet/small room) with the unconfined space. Each opening |
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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 CONFINED |
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SPACES; ALL AIR FROM OUTDOORS. |
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Outside air inlets shall be a minimum of 12” (30 cm) above the grade (snow) line. |
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When supplying air directly from the outdoors: |
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For American installations: Two openings (top and bottom) shall be provided with |
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each opening having a minimum free area of one square inch per 4,000 BTU/hour |
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input (5.5 cm²/kW) of total input rating of all appliances in the confined space. |
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For Canadian installations: Canadian codes specify single air supply source. |
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Canadian customers and authorities having jurisdiction may use the sizing listed in |
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Table 2. When using a single air supply, the duct shall terminate within 1 foot (30 |
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cm) above and within 2 feet (60 cm) horizontally from the burner level of the |
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appliance having the largest input. |
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Table 2 |
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| Combined input of | Required | Acceptable equivalent |
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| all appliances in | free area |
| duct diameter |
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| confined space | of duct |
| A1 | B2 |
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| BTU/hr(kW) | in2(cm2) |
| in(mm) | in(mm) |
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| 25,000(8) | 7(45) |
| 3(75) | 4(100) |
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| 50,000(15) | 7(45) |
| 3(75) | 4(100) |
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| 75,000(23) | 11(70) |
| 4(100) | 5(125) |
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| 100,000(30) | 14(90) |
| 4(100) | 5(125) |
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| 125,000(37) | 18(120) |
| 5(125) | 6(150) |
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| 150,000(45) | 22(140) |
| 5(125) | 6(150) |
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1. Maximum length of ducts in column A is 20 equivalent feet (6.1 meters). |
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2. Maximum length of ducts in column B is 50 equivalent feet (15.2 meters). |
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(c) EQUIPMENT LOCATED IN CONFINED SPACES; ALL AIR FROM |
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OUTDOORS. |
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For American installations: When supplying air directly from the outdoors using |
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horizontal ducting, each opening shall have a free minimum area of one square |
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inch per 2,000 BTU/hour (11 cm²/kW) of total input rating of all appliances in the |
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confined space. |
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For Canadian installations: Refer to Table 2 of part (b). |
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(d) EQUIPMENT LOCATED IN CONFINED SPACES; ALL AIR FROM | *U.S. installations require a dual duct system. | |||||||
OUTDOORS THROUGH VENTILATED ATTIC. | ||||||||
For American installations: When supplying air directly through vertical ducting, | Figure 3: EQUIPMENT LOCATION AND | |||||||
each opening shall have a free minimum area of one square inch per 4,000 | ||||||||
COMBUSTION /VENTILATION AIR | ||||||||
BTU/hour (5.5 cm²/kW) of total input rating of all appliances in the confined space. | ||||||||
REQUIREMENTS | ||||||||
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