A check valve is a ventilation element mounted on the fan body, preventing air from backing into the room. Valve designed for models: pRim pRemium pRestige aRid aRc When the fan is not running, air from the ventilation system or from the outside can enter the bathroom, causing a number of adverse effects – from cooling the room, getting dirty air in winter to transporting fungi and mold that have nested in the ventilation system. The check valve ensures that air flows in only one direction without significantly compromising fan performance. **