Belt drive whole house fan with white powder-coat finish shutter. 2-speed, thermally protected 1/3 HP (horsepower) PSC (Permanent Split Capacitor) 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-out installation. Ceiling mount application only. Dual ball-bearing technology. Tough steel motor struts. Steel venturi for enhanced durability. 24" whole house fan is appropriate for homes with up to 1800 sq ft (square foot) 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 3200 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" whole house fans. Center vein is stationary to allow no-cut joint installation. 10 year limited warranty.