I recently moved to Berlin, Germany and I have this white tube above the window in my apartment. There an opening at the top of it where cold air comes out of. On the right it says "midi".

What is it, why is it there, how does it work and can I safely "close it" (if that's possible and a good idea)?

I guess it's there to get some fresh and cold air and avoid mold, but airing out the apartment twice a day should be enough, no?

I tried moving the little white lever thing that's on the right, and things are certainly moving a bit, but I'm not sure if it's supposed to move left, up or down, if at all, and it seems fragile enough to break if I try to move it the wrong way.

I hope this is the right place for this question.

  • "airing out the apartment twice a day should be enough, no?" Yes, it is. Whatever this is, it is meant to add convenience, it's not necessary.
    – nvoigt
    Commented Mar 17, 2020 at 14:44
  • Is there any issue? Commented Mar 22, 2020 at 18:38

1 Answer 1


Lucky you added midi to your question.

It allows a regulated input of fresh air without having to open a window.

The previous renter probably left it there.

See product information (in English) below.


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