The bathroom must be ventilated regularly, otherwise mold will settle. Sometimes it's not that easy, especially if the bathroom doesn't have a window. The solution is a ventilation system or an exhaust system.
Transport used air outside
Regardless of whether your bathroom has a window or not, the humid air that is created when showering, bathing or drying clothes must definitely be transported outside. One possibility is to ventilate well. This also works if the bathroom does not have a window by opening the windows in the two rooms next to the bathroom and the bathroom door. Then the water vapor escapes from the bath and is directed outside. But a ventilation system is better.
Central exhaust system
You install the central exhaust air system if your bathroom has no windows and no access to an outside wall. This ventilation system is based on the fact that the air from the bathroom is discharged outside through the existing ventilation shaft or pipes with the help of a fan. This fan does not provide fresh air. This comes, for example, by ventilation slots in the door to the bathroom.
So that the right amount of air is replaced, you must select a corresponding device. The right exhaust air device can be found by calculating the exhaust air for your bathroom.
Central ventilation system
The central ventilation system leads the exhaust air through a wall breakthrough into the open and supplies the bathroom at the same time with fresh air. Such a system makes sense, even if you have windows in the bathroom, because it works reliably. For example, after bath use, you can leave the house immediately and do not have to open the window and wait for a while to close it. Nevertheless, they should also do that sometimes, because so the fresh air leads to the bathroom and gets faster removed faster.