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

I totally agree with you. Personally, I would also prefer gas. However, in most new development areas – like ours – unfortunately no pipes are being laid anymore.

So the only options left are the air source heat pump, air-water heat pump, or ground-water heat pump...

It might be interesting to consider the topic of liquid gas. In our case (gap in an older development area), natural gas is offered, but if there is enough space, I would also consider liquid gas for a new building.

is (unfortunately) right in practice. Especially if you don’t take care of it in time..

For a well and efficiently running heat pump, due to the lack of motivation and knowledge of most heating engineers, self-initiative is required.

That means:
Have a proper heating load calculation done.
Have the underfloor heating designed according to the heating load calculation with a maximum flow temperature of 32 degrees Celsius.
Probably use wall heating in the bathrooms.
Matching heating circuits with about 80 meters per circuit.
Omitting buffer storage and bypass valve.
Adjustment and balancing of the system in the first winter.

It often already fails at the heating load calculation, because the experienced heating engineer still estimates. This results in massively oversized units being installed.
The calculation of the underfloor heating is the same. Nobody wants to invest time there.
In addition, heating engineers often add a large markup on the heat pump price during the sale. Which makes the heat pump particularly unattractive.

If you consider the above points, you get a heating system with which you never have to adjust anything again after the first winter and which is extremely low-maintenance. This keeps the follow-up costs very manageable. As long as you don’t have a fireplace, you will never see the chimney sweep again, can save the basic gas fee and the connection fee as well.
Replacing the heat pump in many years is also very easy to manage. A few cables and two pipes.

However, the system from does not seem to run really well despite all optimization. Apart from that, providing hot water via solar is not free, because the solar thermal system had to be purchased and installed.

Conclusion: I am an interested layperson and would pay attention to the above-mentioned requirements anyway in order to remain flexible in the future.
For me, only a heat pump in a new building would be an option.
Gas is simpler. The heating engineer’s planning errors do not matter as much on the operating cost side.

I am not a fan of liquefied gas. You have the tank issue, the higher fuel price compared to natural gas, and then it still has to be transported to you by ship and truck. All in all, not nice, so preferably regional and pellet heating.

I think my heating is running not too badly now. 60 euros on average is probably the norm, of course it can be better. But I am satisfied, much depends on usage behavior. We like it warm and the new building takes a few years to dry out. So it will certainly go down a bit.

hits the nail on the head with what I want to add. When determining the heating demand, please don’t lie to yourself. Schwörerhaus used standard values, which means living room 21 degrees, bedroom I think 19, etc. But honestly, that’s too cold for me. I always sit at home in winter in shorts and a T-shirt; I don’t want to use blankets. So our consumption is probably 20-30% higher than comparable houses "room temperature 23 degrees." I was not aware of the effects; at that time, I didn’t know anyone who had installed an air-to-water heat pump. Only heard about it and the salesperson. If I had known the forum back then, I would have gone with gas, although personally, I am a bit averse to it. It annoys me a bit because I have actually been on the internet since 1996 and was also registered in various forums before, where you really get very informative posts directly from users and not from salespeople.

What does an air-to-water heat pump actually consume per year on average?

Would 3,000 kWh p.a. be sufficient? How can you calculate something like that?

*Kfw 40-Plus, 180 m² living space., fireplace, underfloor heating, controlled residential ventilation, 21-22 degrees consistently in all rooms or bathroom (a total of 21 m²) 23-24 degrees

Obviously, this depends on the manufacturer/model among other things. But there should somehow be a "rule of thumb" for it, right?

Rule of thumb: check the energy certificate under "final energy demand." Roughly add 20 to 30% (user-dependent) and divide by the annual performance factor of the air-water heat pump and multiply by the heated area.