No direct-gas-fired makeup-air heater may be located in any hazardous use room, nor may the discharge from a direct-gas-fired makeup-air heater be directed into a hazardous use room unless the unit shall be designed to insure that flow velocity at the outlet of the unit can never fall below 200 feet per minute, in order that there can be no possibility of backflow of air from the room.
(Prior code § 60-21)