Gravity Ventilator, Low Profile, Fan Size: 42", Fan Not Included, Damper Size: 43" X 43", Base Dims: 461/2" X 461/2", 5633/460 CFM/Throat Velocity @ 0.050-In SP Gravity Intake, 6229/650 CFM/Throat Velocity @ 0.100-In SP Gravity Relief, 8907/727 CFM/Throat Velocity @ 0.125-In. SP Gravity Intake, 11,267/920 CFM/Throat Velocity @ 0.200-In. SP Gravity Intake, 12,597/1028 CFM/Throat Velocity @ 0.250-In. SP Gravity Intake, Max Intake CFM/Throat Velocity 15,476/1214, Construction Material: Galvanized Steel, Designed For Applications That Require Nonpowered Ventilation Or Can Be Used In Conjunction With Powered Exhaust, Supply, Or Reversible Fans, Weathertight Hood Is Constructed Of Interlocking, Arched, Galvanized Steel Panels, Bird Screen And Hood Come Preassembled, Base Requires Field Assembly With Included Hardware, Overall Dims: 401/2"H X 78"W X 78"D, Weight: 406 Lbs, In Bulk, Made In USA.