Plastic louvered wall shutter with a duct connection for 4" ducting
There are times when an exterior hood on a wall is just too much stuff sticking out of the side of the building. A louvered cover such as this one is a compromise. When the fan turns on, the exiting air flow pushes the three louvers open. Gravity will drop them back into place when the flow stops. Back-flows, air trying to push into the building, are blocked. The louvers are fairly light weight in order to restrict the exiting airflow as little as possible. That means that the louvers are likely to be slightly open much of the time.
The metal sleeve accomodates 4" ducting.