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Page 12
SECTION 4.
Installation
(continued)
4.3 Combustion Air
Mascot ST 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.
A Mascot ST unit can take combustion air from the
space in which it is installed, or the combustion air
can be ducted directly to the unit. Ventilation air
must be provided in either case.
4.3.1 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, which follow.
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" (300mm) of the top and one commencing
within 12" (300mm) 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.
MATERIAL
ABS
PVC, sch 40
CPVC, sch 40
Polypropylene
S ingle wall galv. steel
Table 2.
Required Combustion Air Pipe Material.
COMBUSTION AIR INSTALLATION STANDARDS
UNITED STATES
ANSI/ASTM D1527
ANSI/ASTM D1785 or D2665
ANSI/ASTM F441
UL1738, ULC S636.
26 gauge
LAARS Heating Systems
Method 2:
One permanent opening, commencing
within 12" (300mm) 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/CGA B149.
4.3.2 Ducted Combustion Air
The combustion air can be taken through the wall, or
through the roof. When taken from the wall, it must
be taken from out-of-doors by means of the LAARS
horizontal wall terminal. When taken from the roof, a
field-supplied rain cap or an elbow arrangement must
be used to prevent entry of rain water.
Use ABS, PVC, CPVC, polypropylene, or galvanized
pipe for the combustion air intake. Route the intake to
the water heater as directly as possible. Seal all joints.
Provide adequate hangers. The unit must not support
the weight of the combustion air intake pipe. Maximum
linear pipe length allowed is shown in
5 allowable linear ft. (1.5m) for every elbow used.
The connection for the intake air pipe is at the top of
the unit.
In addition to air needed for combustion, air shall also
be supplied for ventilation, including air required for
comfort and proper working conditions for personnel.
Air pipe material must be chosen
CPVC, sch 40, ANSI/ASTM, Polypropylene
based upon the intended application of the water heater.
Table
6. Subtract
CANADA
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