Opinions about the offer

Knee wall.
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I hope this is not too much for you!

- 150L hot water storage (or 171L)... a few years ago the standard was still 300L...

That's okay, with a heat pump the water has lower temperatures, so a smaller tank is better for hygiene. Only if you really need a lot of hot water at once daily would 300L make sense (large bathtub + showers afterwards). I would rather try to do without the buffer tank, because it increases electricity consumption permanently and it has no benefit if the individual room control is not used (which is recommended).

That's too much for me... I think only a construction expert for fees can see the latent errors anyway.

That is okay, with a heat pump the water has lower temperatures, so a small storage tank is better for hygiene.

Then it is 171 liters. All good.

150L is too little for gas including solar, but the general contractor offers it. And that shows that you should actually check everything.

No problem, I also do not expect the pages to be taken apart here! But maybe there are a few small obvious things that a layman wouldn't notice! It's just the first offer and nice to hear other experiences or opinions on top of that. I don't expect anyone to examine the part thoroughly! We also understand that we would have such a construction description checked by a professional.