Make-up Filtered Fresh Air Supply centrifugal fans for commercial and industrial use. PennBarry's Muffan replaces foul or contaminated air that is removed by a building's exhaust system. Such make-up air is so essential that it is part of safety and building code requirements for commercial kitchens, chemical laboratories, electrical control rooms and where gas equipment is installed. Proper make-up air provisions should be part of every building plan.