Louver Damper, Adjustable, 18H x 18W, DAYTON, Mfr# 20UA21

21 In.H 21 In.W Drnbl Extrd Alu Combo Dmpr, Louver Type Combination, Frame Type Flanged, Outside Height 17 1/2 in, Outside Width 17 1/2 in, Rough Opening Height 18 in, Rough Opening Width 18 in, Louver Maximum Intake 779 cfm, Maximum Exhaust 1,114 cfm, Flange Width 1 1/2 in, Free Area 0.7 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 15 3/4 in, Number of Blades 3