I live in an older apartment in Berlin and the windows are just terrible - in winter there's drafts coming in everywhere. Now I've been thinking about installing one of those decentralized ventilation systems like the Valliant RenoVent or something similar. Am I allowed to do that as a tenant without asking, or do I need to ask the landlord first?
You definitely shouldn't install this without asking first - modifications like this typically require the landlord's permission and can cause real problems with your landlord. You need to ask beforehand and ideally get written permission, otherwise you risk having to undo everything in the worst case.
Building it in without permission is definitely not a good idea. But here's the thing: it's not automatically subject to approval like a wall opening or something - decentralized ventilation systems are often considered routine maintenance or modernization, so there's way less drama than people think. Talk to your landlord, show him that it's reversible (meaning you can remove it without any damage) and that it actually saves energy. A lot of landlords are more flexible about it if you handle it the right way, rather than sneaking around drilling holes.
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