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6
TABLE - B
Minimum Recommended Combustion
AIR SUPPLY TO MECHANICAL ROOM
Btu/hr
Input
1,500,000
375 in
2
(2419 cm
2
)
425 in
2
(2742 cm
2
)
500 in
2
(3226 cm
2
)
500 in
2
(3226 cm
2
)
567 in
2
(3658 cm
2
)
667 in
2
(4303 cm
2
)
1,500 in
2
(9,677 cm
2
)
1,700 in
2
(10,968 cm
2
)
2,000 in
2
(12,903 cm
2
)
1,700,000
2,000,000
Outside Air*
2 - Openings
Outside Air*
1 - Opening
Inside Air
2 - Openings
*Outside air openings shall directly communicate with the outdoors. When combustion air is drawn from the out side 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 boiler 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. 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 CAN/CGA B149. Check all local code re quire ments for combustion
air.
Combustion Air Source
FIG. 7 Combustion Air from Interior Space
FIG 8 Combustion Air from Outside - Single Opening
3. If air is taken from another interior space, each of the two
openings specified above should have a net free area of one
square inch for each 1000 Btu (22 cm
2
per kW) of input,
but not less than 100 square inches (645 cm
2
).
4. If a single combustion air open ing 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 (7 cm
2
per kW). This opening must be located within 12"
(30 cm) of the top of the enclosure.
CAUTIONƽ
Under no circumstances should the mechanical room 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 unit.