Belt Drive Whole House Fan With Automatic ShutterBelt drive whole house fan with white powder-coat finish shutter. 2-speed, thermally protected 1/3 HP PSC motor. Precision balanced aluminum fan blade assembly. 4 fan blades for greater air movement. Includes 2-speed switch and wall plate. Joist-in or joist installation. Ceiling mount application only. Dual ball-bearing technology. 24" whole house fan is appropriate for homes with 1200 to 2000 sq. ft. attics. Requires a minimum of 8 to 10 sq. ft. of net free air exhaust vent area. 30" whole house fan is appropriate for homes with 2000 to 3000 sq. ft. attics. Requires a minimum of 10 to 12 sq. ft of net free air exhaust vent area. 36" whole house fan is appropriate for homes with attics over 3000 sq. ft. Requires a minimum of 12 to 14 sq. ft of net free air exhaust vent area. Veins run lengthwise on 24" and 30" - crosswise on 36". Center vein is stationary to allow no-cut joint installation. 10 year limited warranty.