Section R. 325.17510 - Combustion air openingsRule 510.
(1) Nonpowered combustion air openings for fuel-fired unit space heaters, steam boilers, and water heaters shall be sized at ½ square inch of net free area per 1,000 Btu per hour input and 1 square inch net free area per 1,000 Btu per hour input for dryers.(2) If powered combustion air supply equipment is used as an alternate to subrule (1) of this rule for water heaters and boilers, then the powered combustion air supply equipment shall be selected to provide not less than 0.33 cubic feet per minute per 1,000 Btu per hour input and shall be electrically interlocked to the combustion controls of each unit.Mich. Admin. Code R. 325.17510