Louver Damper Adjustable 18H x 48W

20.5 In.H 50.5 In.W Drnbl Extrd Alu Combo Dmpr Louver Type Combination Frame Type Flanged Outside Height 17 1/2 in Outside Width 47 1/2 in Rough Opening Height 18 in Rough Opening Width 48 in Louver Maximum Intake 2 337 cfm Maximum Exhaust 3 341 cfm Flange Width 1 1/2 in Free Area 2.1 sq ft Beginning Point of Water Penetration 1 118 fpm Maximum Air Velocity 3 000 fpm Blade Angle 45 Degrees Material Aluminum Inside Height 16 1/2 in Inside Width 45 3/4 in Number of Blades 3