Wind-Driven Turbine Exhaust Ventilator Bracing Location External Head Diameter 31 5/8 in Throat Diameter 20 in Airflow @ 4 mph 1 700 cfm Metal Material Thickness 20 ga 24 ga Overall Height 25 1/4 in Overall Width 31 5/8 in Housing Material Steel Bearing Type Lower Thrust Ball Bearing Oilless Bronze Upper Bearing Bracing Material Steel Housing Finish Galvanized Includes - Installation Requirements Base for New Installations Flashing