House construction according to the Building Energy Act still acceptable or better KFW55

It is always a question of the price-performance ratio. Nowadays, one should plan for a photovoltaic system + heat pump (preferably a brine-water heat pump). Add controlled residential ventilation and you are not far from kfw 55 or even better. I would not rely on a gas boiler nowadays...

We would have an air-water heat pump and photovoltaic preparation (in case there is ever funding for retrofitting)

We would have an air-to-water heat pump and a photovoltaic preparation (in case there is ever a subsidy for retrofitting)

Air-to-water heat pump means having the ugly outdoor unit outside. You have to decide that yourself. Besides, it is not as efficient as the ground-to-water heat pump. I would do photovoltaic right away. With subsidies, the price of photovoltaics will also increase, so you won't benefit much from it.

Air-to-water heat pump means having the ugly outdoor unit outside. You have to decide for yourself. Besides, it is not as efficient as the ground-to-water heat pump.

Will you quickly recoup the additional cost of maybe T€ 10 (just a number) in heating costs? Instead of €500, only €450 in heating costs would mean you have to wait 200 years for amortization.

P.S. I think ground-to-water heat pumps are great and had one in the last house, but it was much more expensive than the air-to-water heat pump in the new house (ground-to-water heat pump not possible, especially not in EL).

Do you quickly recoup the additional cost of maybe T€ 10 (just a number) with the heating costs? Instead of 500€, only 450€ heating costs would mean that you have to wait 200 years for amortization.

P.S. I think ground water heat pumps are great and had one in the last house, but it was much more expensive than the air-to-water heat pump in the new house (ground water heat pump not possible, especially not in EL).

For us, there were no additional costs for the ground water heat pump with surface collectors. Yes, with deep drilling it would have been around €6,000. We would have taken it anyway. However, the property is in a water protection area.

There were no additional costs with the brine-water heat pump with ground collectors for us.

I'm glad to hear that. Normally, there is always a surcharge – after all, the ground collector does not install itself and represents extra effort.

Air-to-water heat pump means having that ugly outdoor unit outside.

There are also purely indoor units. But that's more for a basement.