The Lambro 4-In. 26-Gauge Galvanized Steel Wall Exhaust Hood Bath Fan Vent with Damper, Wire-Mesh Screen, and 11-In. Pipe is ideal for venting through the wall. It features an opening and closing damper that prevents outside elements and air from entering the vent. The damper seals the vent opening when the bath fan is not running because no exhaust air exits the vent. When the appliance operates, the exhaust air pressure pushes the damper open to let the exhaust air escape from the vent. A preinstalled screen prevents critters from entering the home through the vent when not in use. The exhaust vent is for new and replacement installations over an existing 4-in. opening. It features an opening with a net-free area of 11 sq. in. When the bug screen is removed, the net-free area of the unrestricted opening becomes 20.5 sq. in. The vent's manufacturing material is 26-gauge galvanized steel for durability and longevity. Make sure to check local building codes before installation.