25 In.H-W 5.75 In.L Aluminum Wall Shutter Damper Application Backdraft For Nominal Duct Diameter Not Applicable Frame Material Aluminum Number of Panels 1 Maximum Air Velocity 2500 fpm Overall Height 25 in Rough Opening Diameter 22 1/2 in Rough Opening Shape Square Fits Fan Diameter 20 in For Duct Shape Not Applicable Free Area 2.5 sq ft Overall Width 25 in Frame Material Thickness 0.8 in Overall Length 5 3/4 in Connection Type Not Applicable Frame Depth 2 1/2 in