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Conventional Combustion Air Supply
A
CAUTION: Use TruSeal combustion air if damaging
airborne contaminants are or may be present in the
heater area. See "Inside Air Contamination"regarding air
contamination.
U.S. Installations
All Air from Inside the Building
The confined space shall be provided with TWO permanent
openings communicating directly with an additional room(s)
of sufficient volume so that the combined volume of all
spaces meets the criteria for a room large in comparison
(NFGC). The total input of all gas utilization equipment
installed in the combined space shall be considered in
making this determination. Each opening shall have
a minimum free area of 1 in.
mm
per kW) of the total input rating of all gas utilization
2
equipment in the confined space, but not less than 100
in.
(645 cm
). One opening shall commence within 12 in.
2
2
(305 mm) of the top, and one opening shall commence
within 12 in. (305 mm) of the bottom of the enclosure. The
minimum dimension of air openings shall be not less than
3 in. (76 mm) in any direction.
All Air from Outdoors
The confined space shall communicate with the outdoors
in accordance with one of the methods below. The
minimum dimension of air openings shall not be less than
3 in. (76 mm) in any direction. Where ducts are used, they
shall be of the same cross-sectional area as the net free
area of the openings to which they connect.
1. Two permanent openings, one commencing within
12 in. (305 mm) of the top, and one commencing
within 12 in. (305 mm) of the bottom of the enclosure,
shall be provided. The openings shall communicate
directly, or by ducts, with the outdoors or spaces
(crawl or attic) that freely communicate with the
outdoors.
a. Where directly communicating with the out-
doors or where communicating to the outdoors
through vertical ducts, each opening shall have
a minimum free area of 1 in.
(550 mm
per kW) of total input rating of all
2
equipment in the enclosure.
b. Where communicating with the outdoors through
horizontal ducts, each opening shall have a
minimum free area of 1 in.
(1,100 mm
per kW) of total input rating of all
2
equipment in the enclosure.
2. One permanent opening, commencing within 12
in. (305 mm) of the top of the enclosure, shall be
permitted where the equipment has clearances of at
least 1 in. (25 mm) from the sides and back and 6 in.
(152 mm) from the front of the appliance. The opening
12
per 1,000 BTUH (2,225
2
per 4,000 BTUH
2
per 2,000 BTUH
2
shall directly communicate with the outdoors or shall
communicate through a vertical or horizontal duct to
the outdoors or spaces that freely communicate with
the outdoors, and shall have a minimum free area of:
a. 1 in.
per 3,000 BTUH (740 mm
2
total input rating of all equipment located in the
enclosure, and
b. Not less than the sum of the areas of all vent
connectors in the confined space.
A
WARNING: Do not use the "one permanent opening"
method if the equipment room is under negative pressure
conditions.
A
CAUTION: All combustion air must be drawn from
the air outside of the building; the mechanical equipment
room must communicate directly with the outdoors.
Canadian Installations
1. Ventilation of the space occupied by the heater shall
be provided by an opening(s) for ventilation air at
the highest practical point communicating with the
outdoors. The total cross-sectional area of such an
opening(s) shall be at least 10% of the area required
in 2. and 3. (below), but in no case shall the cross-
sectional area be less than 10 in.
2. For heaters using a barometric damper in the
vent system there shall be a permanent air supply
opening(s) having a cross section area of not less
than 1 in.
per 7,000 BTUH (320 mm
2
and including 1 million BTUH, plus 1 in.
BTUH (160 mm
per kW) in excess of 1 million BTUH.
2
This opening(s) shall be either located at or ducted to
a point not more than 18 in. (457 mm) nor less than 6
in. (152 mm) above the floor level. The duct can also
"goose neck" through the roof. The duct is preferred
to be straight down and terminated 18 in. (457 mm)
from the floor, but not near piping. This air supply
opening requirement shall be in addition to the air
opening for ventilation air required in 1. (above).
A
WARNING: Care must be taken to ensure that
the equipment room is not under negative pressure
conditions.
3. For heaters not using a barometric damper in the
vent system, and when air supply is provided by
natural air flow from outdoors for a power burner and
there is no draft regulator, drafthood or similar flue
gas dilution device installed in the same space, in
addition to the opening for ventilation air required in
1., there shall be a permanent air supply opening(s)
having a total cross-sectional area of not less than
1 in.
for each 30,000 BTUH (74 mm
2
total rated input of the burner(s), and the location of
the opening(s) shall not interfere with the intended
purpose of the opening(s) for ventilation air referred
to in 1. This opening(s) can be ducted to a point not
per kW) of the
2
(65 cm
).
2
2
per kW) up to
2
per 14,000
2
per kW) of
2
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