Question about heat demand determination and flow temperature

I find the pipe length quite high for the small area - we have a laying distance of 10-15cm depending on the room and installed just under 1300m - with 22 or 23 heating circuits and about 240m2 heated area...

Oh dear, then we have probably exaggerated it completely for some with about 10m of pipe per m² of heated area (on average). In total, we have just under 160m² heated area and laid almost three 600m rolls. In the bathroom, however, also 2 circuits and virtually laid with zero spacing, otherwise about 7.5 cm.
At 0° outside, we have about 28° flow temperature and the living room has a cozy temperature of 24 degrees...



That would roughly correspond to the 10m per 1m² heated floor area.

I don't find 24 degrees cozy anymore, so ;)

I also think a 7.5 cm laying distance is completely excessive. but if you like it :).

Oh, the pipe was there and paid for, so we installed it too, it supposedly can’t have a negative impact as long as the loops don’t get too large. Generally, however, the heating coils should be laid so closely that the house can also be heated later with another heating system. Designing the spacing so that you (currently with gas) need 40 degrees flow temperature doesn’t really seem sensible and far-sighted to me...

No, not for me either - but for that, you don't need such small distances. For us, with a heat pump, 20cm was calculated in most rooms.

However, we installed 15cm and less in the bathrooms.

Thank you for your many contributions, my wife got in touch with the supplier of the heating and the material who also does the calculation, and had a very informative conversation where all questions were clarified. We are sticking with the installation spacing 10-15 and only in the hallway 15-20 will be installed. That was all already finished the day before yesterday and today the screed is coming, I am curious.