Experiences with brine heat pump

One might think that Vaillant can do that... it is also listed with its 85%, 1.5 kW output for compensating the ventilation but that is too much. Furthermore, the blower door result was set at 1.5 and not 0.66.

We do not have ERR, no buffer tank, everything goes directly into the underfloor heating - the hydraulic balancing was done roughly. The contractor will come again and take a closer look and adjust, he said. However, I don’t really have the problem that heat accumulates and it is roughly equally warm everywhere.
Currently, the energy integral is at -30 min and the brine temperatures are 2.8 °C and 1.1 °C (it will run for about 10 more minutes until the end of the cycle).
Supply / return of the heating - I don’t even know if I can see them.

The 65sqm in the basement are unheated? Or partially heated? Do you still have a door to the basement or an open staircase?

Currently, 65sqm of the basement are unheated. But the stairwell is open and all basement doors are open because of the pets. I would wait with a "rating" for B. until everything is properly adjusted and balanced. For the hydraulic fine-tuning, the temperatures are good at the moment, but that takes quite a while because a house really reacts slowly to small changes in the heating settings.

. Is there underfloor heating or radiators installed in the basement? Or is it purely a "cold basement"?

I have installed a radiator+"ventilator" combination in the rooms there because I only use the rooms (workroom/hobby room etc.) intermittently (e.g. a few hours in the evening), so I can raise the air temperature relatively quickly (even with a low flow temperature) (there are only 4-5 degrees difference in the worst case).

Did you connect the radiators electrically or to the supply line of the sub-distribution of the underfloor heating? Did you have problems with the KFW application because of the "non-heating" of the basement?

The radiators are in the same circuit as the underfloor heating. No problems with the KFW application. There is also no requirement at all on how to heat what, only ht and qp have to be correct.