John Wood Atmospheric Gas (Non-FVIR) - Manual (Page 4)

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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
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 CONFINED
SPACES; ALL AIR FROM OUTDOORS.
Outside air inlets shall be a minimum of 12” (30 cm) 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 2. When using a single air supply, the duct shall terminate within 1 foot (30
cm) above and within 2 feet (60 cm) horizontally from the burner level of the
appliance having the largest input.
Table 2
1. Maximum length of ducts in column A is 20 equivalent feet (6.1 meters).
2. Maximum length 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 outdoors 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 2 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 appliances in the confined space.
Figure 3: EQUIPMENT LOCATION AND
COMBUSTION /VENTILATION AIR
REQUIREMENTS
A
1
B
2
BTU/hr(kW) in 2 (cm 2 ) in(mm) in(mm)
25,000(8) 7(45) 3(75) 4(100)
50,000(15) 7(45) 3(75) 4(100)
75,000(23) 11(70) 4(100) 5(125)
100,000(30) 14(90) 4(100) 5(125)
125,000(37) 18(120) 5(125) 6(150)
150,000(45) 22(140) 5(125) 6(150)
Combined input of
all appliances in
confined space
Required
free area
of duct
Acceptable equivalent
duct diameter
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.
*U.S. installations require a dual duct system.
*
*