The Lambro® 4-In., 26-Gauge Paint-Grade Galvanized Wall Exhaust Hood Vent with Damper, Wire Mesh Screen, and 11-In. Pipe is 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 1/4-in. wire mesh 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 wire mesh screen is removed, the net-free area of the unrestricted opening is now 20.5 sq. in. Constructed from 26-gauge paint-grade steel, this vent is built for durability and long-lasting performance. Make sure to check local building codes before installation. Not for use with clothes dryer venting.