Intake Louver Drainable with Flange Louver Max Exhaust 3843 cfm Louver Max Intake 2688 cfm Intake Louver Outside Height 20-1/2 In. Intake Louver Inside Width 39 In. Louver Free Area 2.607 sq. ft. Louver Material Extruded Aluminum Min Wall Opening (In.) 18H x 42W Flange Width (In.) 1-1/2 Number of Blades 3 Inside Height (In.) 12 Max Velocity (FPM) 3500 Outside Width (In.) 44-1/2 Blade Angle (Deg.) 45 For Use With Intake or Exhaust Applications Includes Bird Screen