Airfoil type wheel that moves the maximum amount of clean air with the minimum horsepower. Aerodynamically designed for maximum efficiency with relatively low tip speed. Quiet operation, non-overloading characteristics. Highest efficiency of all centrifugal fan designs. Scroll-type housing designed to permit efficient conversion of velocity pressure to static pressure, thus permitting a high static efficiency. Highest efficiencies occur 50% to 65% of wide open volume. The horsepower curve reaches a maximum near the peak efficiency area and becomes lower toward free delivery, a self-limiting power characteristic as shown. General heating, ventilating and air conditioning systems. Used in large sizes for clean air industrial applications where power savings are significant. 1600-380,000 CFM single width; 2800-650,000 CFM double width. Static Pressures to 30".