A boiler room shall have a permanent source of outside air to: Permit satisfactory combustion of fuel; and Provide proper ventilation of the boiler under normal operating conditions. Louvered area. The total requirements of all burners for all fired pressure vessels in a boiler room shall be used to determine the louver sizes, whether the pressure vessels are fired by coal, oil, or gas. The minimum net free louvered area shall be at least 1 square foot. The minimum dimension of air openings may not be less than 3 inches. Ducts, when used, shall be of the same cross-sectional area as the free area of the openings to which they connect. The following configurations shall be used: Two permanent openings: One opening shall start within 12 inches of the ceiling, and one opening shall start within 12 inches of the floor; The openings shall connect directly, or by ducts, with the outdoors or with crawl or attic spaces that freely connect with the outdoors; Where directly connecting with the outdoors or where connecting to the outdoors through vertical ducts, each opening shall have a minimum free area of 1 square inch per 4,000 Btu per hour of total input rating, or total relieving capacity, of all fired pressure vessels, whichever is greater; and Where connecting to the outdoors through horizontal ducts, each opening shall have a minimum free area of 1 square inch per 2,000 Btu per hour of total input rating, or total relieving capacity, of all fired pressure vessels, whichever is greater; or One permanent opening: The opening shall start within 12 inches of the ceiling; The opening shall directly connect with the outdoors, or shall connect through a vertical or horizontal duct to the outdoors or with crawl or attic spaces that freely connect to the outdoors; and The opening shall have a free open area of 1 square inch per 3,000 Btu per hour of total input rating, or total relieving capacity, of all fired pressure vessels, whichever is greater. The following table shall be used to determine the net louvered area in square feet: Mechanical Combustion and Ventilation. Mechanical ventilation may be used to supply combustion air or ventilation air, or both, to a boiler room. When mechanical ventilation is used: The firing device shall be interlocked with the fan so that the firing device cannot operate without proven airflow; The velocity of the air passing through the louvers cannot exceed 500 feet per minute; and The total air delivered shall be equal to or exceed 0.5 CFM per 1,000 Btu per hour of total input rating or total required relieving capacity, whichever is greater. Water Heater Combustion Air Ventilation Requirements. Hot water heaters in excess of 200,000 Btu per hour up to but not including 1,000,000 Btu per hour, that are located in their own equipment room, shall have at least: 1 permanent source of outside air; and 1 square foot of total net free louvered air space. Hot water heaters of 1,000,000 Btu per hour or greater shall follow manufacturer's requirements. Hot water heaters with inputs and required relieving capacities less than 200,000 Btu per hour are not covered by this regulation.