Small single-family house with approx. 140m² - any improvement suggestions?

I would definitely leave out the window in the utility room / technical room, so much space for storage is lost there. If not for connections and [LWWP] or [Kontrollierte-Wohnraumlüftung] then you are happy about every shelf etc.

Then you really went for a proper installation if you have a unit like that. For a normal installation, 55cm wide and 110cm high should be enough. I think the suggestion with the small utility room from above is great. That way, you still have a storage or junk room upstairs – which you completely lack. The utility room downstairs is too small for that, and I fear the office would otherwise have to be sacrificed for that. I find a walk-in closet unnecessary anyway if the bedroom offers enough space.

Actually nothing special. It's air because no arc fault circuit interrupters are installed. Reducing it by half was not possible. Still, it will be tight even for your dimensions.

Evening everyone,

thanks again to all! Especially kaho674, the floor plan actually made us rethink things once more.
We can leave the utility room on the ground floor as is if the laundry goes upstairs. That seems to be the general consensus.

Attached is a slightly adjusted floor plan from kaho674. What do you think?
- Are there any possibilities for improvement? We’re still not quite sure about the bathroom. (The wall at the toilet should only be half-height)
- We’ll need water upstairs in the utility room as well. So we need a shaft from below, right? How much space does such a shaft take up? Where could it be positioned? Or can the wastewater also go under the floor towards the bathroom?
- In the ground floor utility room the window is very narrow in height. There should be enough space for the equipment then, right?
- The positioning of the windows on the right side is probably not optimal. The windows on the upper floor should be floor-to-ceiling. (I can’t manage to draw that at the moment ops

But the exterior view already looks a bit ugly, doesn't it?...

Yes, somehow
Attached again with floor-to-ceiling windows...

Yes, that looks poor. It won't be perfect for me either, but I would say it will be somewhat better: