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TABLE - B
Minimum Recommended Combustion
AIR SUPPLY TO MECHANICAL ROOM
Combustion Air Source
Btu/hr | Outside Air* | Outside Air* | Inside Air |
Input | 2 - Openings | 1 - Opening | 2 - Openings |
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1,500,000 | 375 in2 (2419 cm2) | 500 in2 (3226 cm2) | 1,500 in2 (9,677 cm2) |
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1,700,000 | 425 in2 (2742 cm2) | 567 in2 (3658 cm2) | 1,700 in2 (10,968 cm2) |
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2,000,000 | 500 in2 (3226 cm2) | 667 in2 (4303 cm2) | 2,000 in2 (12,903 cm2) |
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*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 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 requirements for combustion air.
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 cm2 per kW) of input, but not less than 100 square inches (645 cm2).
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 (7 | cm2 | |||
per kW). This opening must | be | located | within | 12" | ||||
(30 cm) of the top of the enclosure. |
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CAUTION
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.
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