40 In.H 28 In.W Non-Drnbl GSteel Intake Louver Louver Type Stationary Blade Frame Type Flanged Frame Depth 4 in Mounting Style Surface Mount Outside Height 40 in Outside Width 28 in Rough Opening Height 36 in Rough Opening Width 24 in Louver Maximum Intake 3 150 cfm Maximum Exhaust 4 500 cfm Maximum Outside Width 40 in Minimum Outside Width 28 in Flange Width 2 in Free Area 3.6 sq ft Beginning Point of Water Penetration 766 fpm Maximum Air Velocity 3000 fpm