Our bathroom fan filter was worn out and very dirty with cigarette smoke from the previous tenant¹, so we removed it. We could replace it, but why does a bathroom fan need a filter in the first place? What harm would be done if we continue using our bathroom fan without a filter?
The bathroom is a windowless room on the inside of an apartment in a 1990s apartment block in Germany with 12 units in the building in total. I suspect the ducts lead to a shared pipe system through which the air goes outside. The fan is a maico, but I don't know the exact model.
I found some discussion in German on focus, urbia, and vermieter-forum, but no clear conclusion, nor does this English language usenet discussion. DIY stores do not appear to have bathroom fan filters widely available, although they do exist for sale, for example at lowes, directly from maico, or on amazon. The product description on amazon claims:
Das Gerät niemals ohne Filter betreiben. Die Verwendung der Filter garantiert:
- Optimale Filterung der Luft
- Lange Lebensdauer Ihres Ventilators
- Perfekte Passform und somit maximale Dichtheit ohne Leckluft filtAIRS
- Luft ist Leben
Never use the device without a filter. The filter guarantees:
- Optimal filtering of the air
- Long lifetime of your fan
- Perfectly fitting and therefore maximal closure without leaking air filtAIRS
- Air is life
Only the second bullet point addresses the need. Does the filter increase the lifetime of the fan?
I recall reading that some people have a problem of bad smells entering their home from the neighbours through the ducts, but I don't know if the filter would be aimed for or effective at stopping this, and it is not a problem we (currently) experience.
¹In Germany, according to vermieter-forum, this would count as a small fix that is the tenants responsibility.