HOME IMPROVEMENT Perfect for use in AC, dryer vent, heating ducts, extractor or range hoods. Especially suitable for using with exhaust fan, bathroom fan, blower fan, attic fan. EASY INSTALLATIONThe duct damper opens and closes automatically, allowing only one-directional airflow. The damper blades open only in the outflowing air direction when the shutter is installed. The duct valve for 4-inch duct best installed in a horizontal position and inserted fully into the duct. This also applies to vertical installation. HIGH-QUALITY MATERIALS The casing of the shutter is made of galvanized steel sheet. The dryer vent valve blades are made of aluminium. The shaft and spring are made of stainless steel. The shutter is able to withstand temperatures up to 140F. GREAT FOR HOME USE The foam sealing on the damper reduces operation noise and provides extra air tightness. The back draught valve can be inserted into a non-flexible metal or plastic duct directly, but for flexible duct you need to use steel duct clamps to secure the backdraft damper.