Gas Engineering Guide

Air – Adequate Volume

If the volume of the room or space in which fuel-burning appliances are installed is equal to or greater than 50 cubic feet per 1,000 Btu/hr of combined input rating of appliances, infiltration may be regarded as adequate to provide combustion air. (NFPA 54,*). Rooms communicating directly with the space in which the equipment is installed may be considered part of the non-confined space as long as openings between them have no doors. Exclude from the calculation the input ratings of listed direct vent appliances, cooking appliances, refrigerators, and domestic clothes dryers.

Minimum Volume Required:
150,000 Btu/hr x (50 cubic feet / 1000 Btu/hr) = 7500 cubic feet

Volume Available:
20 x 30 x 8 = 4800 cubic feet

Since the volume available in the room is smaller than the minimum required for proper ventilation, this room would be considered a confined space and combustion air would be required.The air supply for gas appliances vented by natural draft, normally may be obtained by application of one of the methods in the following sections (Unconfined Spaces, Confined Spaces, Outside Air).

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