HUMIDIN high efficient Plug Fans, with backwardly inclined curved wheels are designed for clean air applications or for moist air systems. The plug fan eliminates the need for connecting ductwork. Its mounting panel permits assembled-unit installation to any well-supported plenum wall. 15 fan sizes from 12ft through 55ft diameter wheels, in Class I, II, III construction. They are available in direct and belt drive configurations at respective sizes.