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HTD
2.C.5 Combustion Air
Boilers and water heaters must have provisions for
combustion and ventilation air in accordance with the
applicable requirements for Combustion Air Supply and
Ventilation in the National Fuel Gas Code, ANSI Z223 1;
or in Canada, the Natural Gas and Propane Installation
Code, CSA B149.1. All applicable provisions of local
building codes must also be adhered to.
This unit can take combustion air from the space
in which it is installed, or the combustion air can
be ducted directly to the unit. Combustion and
Ventilation air must be provided in either case.
2.C.5.a Combustion Air From Room
In the United States, the most common requirements
specify that the space shall communicate with the
outdoors in accordance with Method 1 or 2. (See the
following descriptions.) Where ducts are used, they shall
be of the same cross-sectional area as the free area of
the openings to which they connect.
Method 1
: Two permanent openings, one commencing
within 12” (30 cm) of the top and one commencing
within 12” (30 cm) of the bottom, of the enclosure
shall be provided. The openings shall communicate
directly, or by ducts, with the outdoors or spaces
that freely communicate with the outdoors. When
directly communicating with the outdoors, or when
communicating to the outdoors through vertical ducts,
each opening shall have a minimum free area of 1
square inch per 4000 Btu/hr (550 square mm/kW) of
total input rating of all equipment in the enclosure.
When communicating to the outdoors through horizontal
ducts, each opening shall have a minimum free area
of not less than 1 square inch per 2000 Btu/hr (1100
square mm/kW) of total input rating of all equipment in
the enclosure.
Method 2
: One permanent opening, commencing
within 12” (300 mm) of the top of the enclosure, shall
be permitted. The opening shall directly communicate
with the outdoors or shall communicate through a
vertical or horizontal duct to the outdoors or spaces
that directly communicate with the outdoors and shall
have a minimum free area of 1 square inch per 3000
Btu/hr (734 square mm/kW) of the total input rating of
all equipment located in the enclosure. This opening
must not be less than the sum of the areas of all vent
connectors in the confined space.
Other methods of introducing combustion and
ventilation air are acceptable, providing they conform to
the requirements in the applicable codes listed above.
In Canada, consult local building and safety codes or, in
absence of such requirements, follow CAN/CSA B149.
