Filter
Top Products
Figure 1-7_Combustion Air from Outside - Single
Opening
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. 1-7).
TABLE - 1B
MINIMUM RECOMMENDED COMBUSTION
AIR SUPPLY TO EQUIPMENT ROOM
Model
Number
FIG. 1-4 FIG. 1-5 FIG. 1-6 FIG. 1-7
*Outside Air from
2 Openings Directly from
Outdoors
*Outside Air from
2 Ducts Delivered from
Outdoors
**Inside Air from
2 Ducts Delivered from
Interior Space
*Outside Air from
1 Opening Directly
from Outdoors, in
2
To p
Opening, in
2
Bottom
Opening, in
2
To p
Opening, in
2
Bottom
Opening, in
2
To p
Opening, in
2
Bottom
Opening, in
2
1.0
250
(1613 cm
2
)
250
(1613 cm
2
)
500
(3226 cm
2
)
500
(3226 cm
2
)
1000
(6452 cm
2
)
1000
(6452 cm
2
)
333
(2149 cm
2
)
1.3
325
(2097 cm
2
)
325
(2097 cm
2
)
650
(4194 cm
2
)
650
(4194 cm
2
)
1300
(8388 cm
2
)
1300
(8388 cm
2
)
433
(2794 cm
2
)
1.5
375
(2420 cm
2
)
375
(2420 cm
2
)
750
(4839 cm
2
)
750
(4839 cm
2
)
1500
(9678 cm
2
)
1500
(9678 cm
2
)
500
(3226 cm
2
)
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.
ƽ CAUTION
Under no circumstances should the
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 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.
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.
Combustion air requirements are based on the latest edition
of the National Fuel Gas Code, ANSI Z223.1; in Canada refer
to the latest edition of CGA Standard CAN B149.1 or B149.2.
Check all local code requirements for combustion air.
12
1 Determine boiler location
Installation & Operation Manual
*Outside air openings shall directly communicate with the outdoors. When combustion air is drawn from the outside through a
duct, the net free area of each of the two openings must have twice (2 times) the free area required for Outside Air/2 Openings.
The above requirements are for the water heater only; additional gas fired appliances in the equipment room will require an
increase in the net free area to supply adequate combustion air for all appliances.
**Combined interior space must be 50 cubic feet per 1,000 Btu/hr input. Buildings MUST NOT be of *“Tight Construction”.
For buildings of *“Tight Construction”, provide air openings into the building from outside.
*No combustion air openings are needed when the water heater 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”.
*”Tight Construction” is defined as a building with less than 0.40 ACH (air changes per hour).
Where two openings are provided, one must be within 12"
(30cm) of the ceiling and one must be within 12" (30cm) of the
floor of the equipment room. Each opening must have net free
area as specified in the chart below (Table 1B). Single openings
shall commence within 12" (30cm) of the ceiling.