12
b. Where communicating with the outdoors
through horizontal ducts,
each opening
shall
have a minimum free area of 1 square inch per
2,000 BTUH (1,100 mm² per kW) of total input
rating of all equipment in the enclosure.
2. One permanent opening,
commencing within
12" (305 mm) of the top of the enclosure, shall be
permitted where the equipment has clearances
of at least 1" (25.4 mm) from the sides and back
and 6" (152 mm) from the front of the appliance.
The opening 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 square inch per 3,000 BTUH (740 mm² 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.
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WARNING:
Do not use the “one permanent opening”
method if the equipment room is under negative-pressure
conditions.
3.6.2. Canadian Installations
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CAUTION:
All combustion air must be drawn from the
air outside of the building; the mechanical equipment
room must communicate directly with the outdoors.
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 below, but in no case shall
the cross-sectional area be less than 10 square inches (65
cm²).
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WARNING:
Make sure that the equipment room is not
under negative-pressure conditions.
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 steps 2 and 3 (below), but in no case shall the
cross-sectional area be less than 10 in.
2
(65 cm
2
).
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.
2
per 7,000 BTUH (320 mm
2
per kW) up to
and including 1 million BTUH, plus 1 in.
2
per 14,000
BTUH (160 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" (450 mm) nor less than
6" (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" (450 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).
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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
above, there shall be a permanent air supply
opening(s) having a total cross-sectional area of not
less than 1 square inch for each 30,000 BTUH (74
mm² per kW) of 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 above.
This opening(s) can
be ducted to a point not more than 18"
(450 mm)
nor
less than 6"
(152 mm) above the floor level. The duct
can also “goose neck” through the roof. The duct is
preferred to be straight down 18" (450 mm) from the
floor, but not near piping.
4. Refer to the B149 Installation Code for additional
information.
3.7.
Water Piping
3.7.1. General
The heater should be located so that any water leaks will
not cause damage to the adjacent area or structures.
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CAUTION:
This heater must be installed with a
Primary-Secondary piping arrangement for the integral
pumping system to function properly.
NOTE:
Minimum pipe size for the heater inlet/outlet
connections is dependent on the equivalent length of
piping between the load loop and the heater loop, the
operating conditions and the size of the heater. See Table
G and Table H.
