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Re: Ventilation requirements for natural gas water heater
Combustion air for gas-burning appliances
Exterior: Direct Openings - 12 inches from ceiling and 12 inches from deck (floor)
Horizontal Direct:
2 openings (Hi / Low) minimum of 1 square inch for each 4,000 BTu (each vent)
Ex: 150 K BTu's (75 square inches)(@ 4K BTu's)
Horizontal Ducts: (to exterior)
2 openings (Hi / Low) minimum of 1 square inch for each 2,000 BTu (each vent)
Ex: 150 K BTu's (37.5 square inches)(@ 2K BTu's)
Vertical: 2 openings (Hi / Low) minimum of 1 square inch for each 4,000 BTu (each vent)(can be to a space i.e. attic that is equivalent to outdoors)
Ex: 150 K BTu's (75 square inches)(@ 4K BTu's)
10 inch diameter pipe (circular) is equal to 78.5 square inches (radius squared * Pi)(25 * 3.14)
Interior:
Indoor air source alone only OK if air infiltration rate (ACH) is greater than 0.4 per hour
Minimum volume of appliance space is 50 Cubic ft per 1000 BTu's
Space (closet) with volume less than 50 Cubic ft per 1000 BTu's is OK only if 2 permanent openings to a space with sufficient volume and infiltration ACH 0.4
Ex: 150 K BTu's (150 square inch opening to unconfined space of 7500 cubic feet)
Local codes may vary.
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