18 in Backdraft Damper / Wall Shutter, 18-1/2 in x 18-1/2 in, DAYTON, Mfr# 4FZH5

21 In.H-W 6.5 In.L Extrd Alu Backdraft Dampr, Damper Application Backdraft, For Nominal Duct Diameter Not Applicable, Frame Material Aluminum, Number of Panels 1, Maximum Air Velocity 3250 fpm, Overall Height 21 in, Rough Opening Diameter 18 1/2 in, Rough Opening Shape Square, Fits Fan Diameter 18 in, For Duct Shape Not Applicable, Free Area 2 sq ft, Overall Width 21 in, Frame Material Thickness 0.8 in, Overall Length 6 1/2 in, Connection Type Not Applicable, Frame Depth 3 in