Buy a house with energy class H and not renovate much?

I never wrote anything about tilted windows, or where do you read that? Blinds down to about 15/20 cm, then leave one pane slightly open behind the curtain.

It’s the same. Sorry.

Heating costs? I like it cool in the bedroom anyway, so the heating is off there.

The cold bedroom is heated through the other rooms. And in an uninsulated old building – this is what this is about – that is also a reason for mold.
You basically do everything wrong for an old building that you can do wrong. Even if it feels good to you.

It's the same. Sorry.

No, it is not. The cold air does not hit the cold wall immediately but can flow into the room because there is still a (closed) window sash next to it. And heating through other rooms can be largely prevented by closed doors. We already had this in the old building, and it worked well without mold.

The cold air does not immediately hit the cold wall, but can flow into the room,

You know that this is nonsense? The air always flows along or past a wall, and all walls in the room cool down.

We already had this in the old building and it worked well without mold.

Just because it worked for you, please do not generalize your procedure. Unfortunately, it is the cause of so many thousands of moldy walls.

Yes, the calculated energy certificate does not match the blown-in insulation, but it does match the actual consumption values given the fact that the ceiling between floors and the basement ceiling are uninsulated and the boiler is poorly adjusted. Well, I think that by insulating the basement ceiling and the attic floor, I can already save something in combination with 33 mm radiators and lowering the flow temperature to 50-60 degrees. Last winter, the house consumed 180 KWH per m2 (according to consumption values or billing at an allegedly 22-24 degrees room temperature in winter and no one was on vacation or anything similar), so I hope to only consume 150 KWH per m2, especially since 21 degrees during the day and 18/19 at night is completely sufficient for me. Of course, I would also renew the glass. With all measures, I would probably spend 30-35K, which is nothing compared to renovations costing well over 400,000€ that I believe will no longer pay off in this lifetime.

You know that's nonsense? The air always flows to a wall or past it, and all walls in the room cool down.

Just because it worked for you, please don't generalize your procedure. Unfortunately, it is the cause of so many thousands of moldy walls.

Yes, tilted windows, not opened ones.

The agent just called me and informed me that another interested party gave a purchase commitment without hesitation during the first viewing.