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. 14 in blade diameter. Rust resistant metal construction. Flashing size 21 in x 22-1/4 in Automatic adjustable thermostat included.