Change floor heating installation spacing

15cm can definitely make sense. Going from flat 15.10 to flat 10.7.5 does not necessarily have to work better.

Yes, so IB Heckmann, for example, also planned only 15cm in my Allraum. If there is already a lot of space anyway, the VA doesn’t always need to be super low. Almost more important is that in small rooms like the bathroom or corner children's room the VA might even be lower than 10cm. For example 7.5cm, but yes, all that needs to be calculated.

15cm can definitely make sense.

But not like the OP does, blanket for the entire house ;) . Then I'd rather go with 10cm across the board and have applied too much, which in the end wouldn't be a problem. But yes, it should must be calculated correctly.

Thank you very much for the assessments. Then I will have the calculations from the GU shown to me for verification by the neighbor (heating engineer master). The GU certainly has to request these calculations from the heating engineer. Does the heating engineer have to provide the calculations to the GU and the GU give me these documents, or is it goodwill if it does?

Depends on what is stated in the contract. As far as I know, something like that is not included in the [Baugesetzbuch].

The general contractor certainly has to request these calculations from the heating engineer. Does the heating engineer have to provide the calculations to the general contractor and the general contractor give me these documents, or is it goodwill if they do so?

He does not have to. But if I am building a house for half a million, I would also like to have the relevant documents on hand. And a heating load calculation and heating system design are basic documents. He who pays the piper calls the tune.