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4. If a single combustion air opening is provided to bring
combustion air in directly from the outdoors, the
opening must be sized based on a minimum free area of
one square inch per 3000 Btu/hr (7 cm
2
per kW). This
opening must be located within 12" (30 cm) of the top of
the enclosure (see FIG. 1-6).
Figure 1-6_Combustion Air from Outside Single Opening
Combustion air require ments are based on the latest edition
of the National Fuel Gas Code, ANSI Z223.1, in Canada refer
to National Standard CAN B149.1. Check all local code
re quire ments for combustion air.
All dimensions are based on net free area in square inch es.
Metal louvers or screens reduce the free area of a combustion
air opening a minimum of approximately 25%. Check with
louver manufacturers for exact net free area of louvers. Where
two openings are pro vid ed, one must be within 12" (30 cm) of
the ceiling and one must be within 12" (30 cm) of the floor of
the room where the appliance is installed. Each opening must
have a net free area as specified in Table 1B (on page 12).
Single openings shall be located with in 12" (30 cm) of the
ceiling.
ƽ CAUTION
Under no circumstances should the room
where the appliance is installed ever be
under a negative pressure. Particular care
should be taken where exhaust fans, attic
fans, clothes dryers, compressors, air
handling units, etc., may take away air from
the appliance.
The combustion air supply must be completely free of any
flammable vapors that may ignite or chemical fumes which may
be corrosive to the appliance. Common corrosive chemical
fumes which must be avoided are fluorocarbons and other
halogenated compounds, most commonly present as
refrigerants or solvents, such as freon, tricholorethylene,
perchlorethylene, chlorine, etc. These chemicals, when burned,
form acids which quickly attack the heat exchanger finned tubes,
headers, flue collectors, and the vent system. The result is
improper combustion and a non-warrantable, premature
appliance failure.
The result is improper combustion and a non-warrantable,
premature appliance failure.
EXHAUST FANS: Any fan or equipment which exhausts air
from the equipment room may deplete the combustion air
supply and/or cause a downdraft in the venting system. Spillage
of flue products from the venting system into an occupied living
space can cause a very hazardous condition that must be
immediately corrected. If a fan is used to supply combustion air
to the equipment room, the installer must make sure that it does
not cause drafts which could lead to nuisance operational
problems with the appliance.
Installation & Service Manual
11
1 Determine boiler location (continued)