A supply of tempered makeup air equal to or greater than the total volume of air being continually exhausted from the dry cleaning plant should be provided in order to eliminate negative pressure conditions which might develop. A tempered makeup air supply is required for all installations of more than four machines, for all installations in buildings with dry cleaning machines only and for all installations where field tests indicate that down-drafting of combustion flues results from operation of the exhaust fan equipment. The tempering capacity of makeup air equipment shall be sufficient to provide a minimum of a sixty degree Fahrenheit temperature rise for the quantity of air being supplied. Where tempered makeup air equipment is not provided, a permanent open louvered area shall be provided to allow air to enter the building. This area shall be sized on the basis of one square foot of net opening per 500 CFM.
(1974 Code § 7.240)