Heiko's place is really amazing. Confortable and cosy, with excellent equipment. We were there in late autumn, but did not feel cold inside.
If you are staying in a large group, be aware that the living spaces and mezzanine are all open, so that when someone is speaking in the kitchen, it moght disturb those sleeping in the mezzanine.
Nevertheless, you will hardly find sich an original accomodation in Berlin for such a good price.