(All Air from Inside the Building)
The confined space shall be provided with two permanent openings, one located within the upper 12 inches of the enclosure and one located within the lower 12 inches of the enclosure. Each opening shall have a free area of not less than one square inch per 1,000 Btu per hour of total input rating of all appliances within the enclosure. (NFPA 54, 126.96.36.199).
The remainder of the building must meet the volume of space required and the interior areas have adequate infiltration from the outside. (See Outside Air)
Openings and ducts shall not connect appliance enclosures with space in which the operation of an exhaust fan may adversely affect the flow of combustion air.
Combustion air supply shall not be obtained from any hazardous location or from any area in which objectionable quantities of flammable vapor, lint, or dust are given off. Combustion air shall not be taken from a refrigeration machinery room.