Hello ato, in principle, decentralized ventilation units with heat recovery that operate in pairs should not be installed in wet rooms. Firstly, they cannot handle the high humidity in winter and freeze up, and secondly, you don’t want the humidity or the odor in your living spaces, right? Therefore, exhaust fans should always be used here, preferably humidity-controlled. The other rooms (living room, bedroom, etc.) can be equipped with these devices without any concern. The wall penetration, usually a plastic pipe, is installed with a slight slope of 1-2% to the outside. If condensation occurs (transitional period), it drains outside. Regards HIGIL