29 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 2250 fpm Overall Height 29 in Rough Opening Diameter 27 1/2 in Rough Opening Shape Square Fits Fan Diameter 24 in For Duct Shape Square Free Area 4.1 sq ft Overall Width 29 in Frame Material Thickness 20 ga Overall Length 4 1/2 in Frame Depth 2 in Rough Opening Length 26 1/2 in