For roof or gable mount. Heavy-duty screen deters animals and insects. Large pre-punched flashing for easier installation and less chance of leaks. 14 attic air exchanges per hour. Air flow of 1000 CFM (Cubic Feet Per Minute) for attics up to 1 600 sq. ft . for optimal perfomance. 14in. blade diameter. Rust resistant metal construction. Flashing size 21-inch x 22-1/4-inch. Automatic adjustable thermostat included; Gaf/master Flow; Color=Mill