21 In.H-W 4.5 In.L Aluminum Backdraft Damper, Damper Application Backdraft, For Nominal Duct Diameter Not Applicable, Frame Material Galvanized Steel, Number of Panels 1, Maximum Air Velocity 2000 fpm, Overall Height 21 in, Rough Opening Diameter 19 1/2 in, Rough Opening Shape Square, Fits Fan Diameter 18 in, For Duct Shape Square, Free Area 1.9 sq ft, Overall Width 21 in, Frame Material Thickness 20 ga, Overall Length 4 1/2 in, Frame Depth 2 in, Rough Opening Length 18 1/2 in Damper Size (In.): 19 x 19;Overall Size (In.): 21 x 21;Flange Width (In.): 1 in;Overall Width: 21 in;Overall Height: 21 in;Overall Length: 4 1/2 in;Frame Depth: 2 in;Rough Opening Length: 18 1/2 in;Fits Fan Diameter: 18 in;For Nominal Duct Diameter: Not Applicable;Overall Diameter: Not Applicable;Flange Width: 1 in;Rough Opening Diameter: 19 1/2 in;Rough Opening Width: 19.5 in; Item: 21"H-W 4.5"L Aluminum Backdraft Damper;Type: Roof Mount, Exhaust;Use w/Dayton Ventilators: 4HX83, 4HX84, 4HX94, 4HX95, 4HZ48, 4HZ49, 4HZ52, 4HZ53, 4YC48, 4YC49, 4YC72-75;Construction Material: Aluminum Blades, G-90 Galvanized Steel Frame, Nylon Bushings and Galvanized Steel Tie Rods., Stainless Steel Pivot Pins;Max. Velocity (FPM): 2,000 fpm;Includes: Pre-Punched Conduit Hole Knock-Out; Felted Edges for Quiet Operation;Outside Flange (In.): 21 x 21;Rough Opening Dims: 18 1/2 in x 19.5 in;Blade: Aluminum Blade w/ Felt Seal;Rough Opening Shape: Square;
