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1
Determine boiler location
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
opening must be located within 12" (30 cm) of the top of
the enclosure (see FIG. 1-7).
Combustion air requirements are based on the latest edition
of the National Fuel Gas Code, NFPA 54 / ANSI Z223.1; in
Canada refer to the latest edition of CGA Standard CAN/CSA
B149.1. Check all local code requirements for combustion air.
All dimensions based on net free area in square inches. 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 provided, one must be within 12"
(30 cm) of the ceiling and one must be within 12" (30 cm) of
the floor of the equipment room. Each opening must have a
net free area as specified in Table 1B. Single openings shall
commence within 12" (30 cm) of the ceiling. The minimum
dimension of air openings shall not be less than 3" (80 mm).
FIG. 1-4
*Outside Air from
2 Openings Directly from
Model
Outdoors
Number
Top
2
Opening, in
(cm
2
)
188
FB 0751
(1213)
250
FB 1001
(1613)
313
FB 1251
(2020)
The above requirements are for the appliance only; additional gas fired appliances in the equipment room will require an increase
in the net free area and/or volume to supply adequate combustion air for all appliances.
No combustion air openings are needed when the appliance is installed in a space with a volume NO LESS than 50 cubic feet per
1,000 Btu/hr of all installed gas fired appliances. Buildings MUST NOT be of *"Tight Construction"
Outside air openings shall directly communicate with the outdoors.
1
Combined interior space must be 50 cubic feet per 1,000 Btu/hr input. Buildings MUST NOT be of *"Tight Construction".
2
"Tight Construction" is defined as a building with less than 0.40 ACH (air changes per hour). For buildings of "Tight
3
Construction", provide air openings into the building from outside.
2
per kW). This
MINIMUM RECOMMENDED COMBUSTION
AIR SUPPLY TO EQUIPMENT ROOM
FIG. 1-5
*Outside Air from
2 Ducts Delivered from
Outdoors
1
Bottom
Top
2
2
Opening, in
Opening, in
(cm
2
)
(cm
2
)
188
375
(1213)
(2420)
250
500
(1613)
(3226)
313
625
(2020)
(4033)
(continued)
Under no circumstances should the
CAUTION
equipment room ever be under 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 unit.
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, trichlorethylene, perchlorethylene,
chlorine, etc. These chemicals, when burned, form acids which
quickly attack the stainless steel heat exchanger, headers, flue
collectors, and the vent system.
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
corrected immediately.
TABLE - 1B
Inside Air from
2 Ducts Delivered from Interior Space
1
Same Story
Bottom
Top
2
2
Opening, in
Opening, in
(cm
2
)
(cm
2
)
375
750
(2420)
(4839)
500
1000
(3226)
(6452)
625
1250
(4033)
(8065)
Installation & Operation Manual
FIG. 1-6
2
*Outside Air from
1 Opening Directly
Different
from Outdoors, in
Stories
Bottom
Total
2
2
Opening, in
Openings, in
(cm
2
)
(cm
2
)
750
1500
(4839)
(9678)
1000
2000
(6452)
(12904)
1250
2500
(8065)
(16129)
.
3
FIG. 1-7
2
(cm
2
)
1
250
(1613)
333
(2149)
417
(2691)
13
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