Exterior mount exhaust fans from Grainger can help ventilate a building's attic and keep damaging moisture from causing mold and mildew. Exterior mounted ventilation fans are mounted on the outside of the building, generally on the roof or on the side of the building. Find durable, reliable exhaust fans that fit ducts 4", 6", 8" and 10" in diameter. Get the exterior mount exhaust fans that fit your needs from Grainger.