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WARNING: Do not use one permanent opening
method if the equipment room is under negative
pressure conditions or the equipment is common
vented with other gas-fired appliances.
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 outdoors. The total cross-sectional area of
such an opening(s) shall be at least 10% of the
area required in (2) and (3), but in no case shall
the cross-sectional area be less than 10 in.
2
(6500
mm
2
.).
2. For heaters using a barometric damper in the vent
system, and when air supply is provided by natu-
CAUTION: All combustion air must be drawn from
the air outside of the building; the mechanical
equipment room must communicate directly with the
outdoors.
Installations in Canada
Water Piping
General
The heater should be located so that any water leaks
will not cause damage to the adjacent area or struc-
tures.
ral air flow from the outdoors for natural draft, par-
tial fan assisted, fan-assisted or power
draft-assisted burners, there shall be a permanent
air supply opening(s) having a cross section area
of not less than 1 in.
2
per 7000 BTUH (310 mm
2
per kW) up to and including 1 million BTUH, plus
1 in.
2
per 14000 BTUH (155 mm
2
per kW) in
excess of 1 million BTUH. This opening(s) shall be
either located at or ducted to a point not more than
18 in. (450 mm) nor less than 6 in. (150 mm)
above the floor level. The duct can also "Goose
Neck" through the roof. The duct is preferred
straight down 18” from floor, but do not place near
piping. This air supply opening requirement shall
be in addition to the air opening for ventilation air
required in (1).
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 sup-
ply opening(s) having a total cross-sectional area
of not less than 1 in.
2
for each 30,000 BTUH (70
mm
2
per kW) of total rated input of the burner(s),
and the location of the opening(s) shall not inter-
fere with the intended purpose of the opening(s)
for ventilation air referred to (1). This opening(s)
can be ducted to a point not more than 18 in. (450
mm) nor less than 6 in. (150 mm) above the floor
level. The duct can also "Goose Neck" through the
roof. The duct is preferred to be straight down 18”
from floor, but do not place near piping.
4. Refer to the latest version of the B149 for addition-
al information.
CAUTION: This heater requires forced water
circulation when the burner is operating. See Table E
and Table F for minimum and maximum flow rates
and water pump selection. The pump must be
interlocked with the heater to prevent heater
operation without water circulation.
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.
2
per
4000 BTUH (5.5 cm
2
per kW) of total input rat-
ing of all equipment in the enclosure.
b. Where communicating with the outdoors
through horizontal ducts, each opening shall
have a minimum free area of 1 in.
2
per 2000
BTUH (11 cm
2
per kW) of total input rating of
all equipment in the enclosure.
2. One permanent opening, commencing within 12
in. (30 cm) of the top of the enclosure, shall be
permitted where the equipment has clearances of
at least 1 in. (2.5 cm) from the sides and back and
6 in. (16 cm) from the front of the appliance. The
opening shall directly communicate with the out-
doors or shall communicate through a vertical or
horizontal duct to the outdoors or spaces (crawl or
attic) that freely communicate with the outdoors,
and shall have a minimum free area of:..
a. 1 in.
2
per 3000 BTUH (7 cm
2
per kW) of the
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.
12