Newly built single-family house KfW55 standard - How to heat?

With that desire, one could also do more with a fan heater for the underfloor heating. Or you set the bathroom directly to 23, after 2 minutes of showering it’s 26 anyway.

With the roughly 30€ per month you calculated, you can supply the whole house including hot water with a heat pump.

Well, that is very optimistic. Currently, I already need 2 to 3 kWh per day for hot water in summer. That is about 18 euros per month. In winter, with heating operation, there are months when the system needs 25 kWh daily, so 800 kWh per month and thus 160 euros. The annual average is more like 60 euros per month. This is now in the optimized state. Previously, with the handover HB, we had an annual average of about 100 euros per month. Ok, we heat 170m2 plus basement, but that is not exactly economical. Latest modulating heat pump on the market.

Would someone actually notice the difference between 21 and 24 degrees? Otherwise, an infrared mirror in the room, it's faster and from the saved costs compared to the electric underfloor heating you can operate the mirror for 50 years.

In the optimized state?
Hot water circulation and poor design of the underfloor heating?

Hot water circulation now only active 10 minutes per day. Design is fine, maybe a heater that is too large was chosen, but the heat load calculation required this. I think a smaller model would be more economical.

That's right. My calculation doesn't convince me either...

There is a lot wrong with the basic understanding of the thermodynamics of a house. Especially when one is considering installing such constructions in a new building.

Design and install a water-based low-temperature underfloor heating system throughout the house according to the wishes. Then heat it with a heat pump or gas.

Use the low-temperature heat pump (LLWP) for cooling in the summer along with shading.