Alternatives to gas, how are they calculated?

That's true, Karsten, in your case. From a 1.5-story building upwards, hardly any visible plastic pipe will run through the bedroom. And no costs are negligible if you want to carry out a full cost accounting. The heat pump faction also likes to portray a heat pump as maintenance-free. That just isn't true.

Thanks for the many responses. You can see – a partly emotional topic...

But if you are already thinking about the price difference between heat pump and gas and how it pays off with the few thousand euros difference, what about the rest of the house?!?

Sure, one could now argue that the few euros don’t make a difference in the total costs, but it doesn’t stop there. In my opinion, this is about a basic attitude, and I am quite clearly of the opinion that I initially leave out everything that doesn’t have to be. The "few thousand euros difference" adds up quite quickly. If you save, reduce, or retrofit a few things here and there, you suddenly save several tens of thousands of euros.

To put that into perspective: Our plot cost over €600 / sqm, with a semi-detached house ready for demolition in an established neighborhood. Putting a house on top of that and despite six-figure equity, we will take out a loan of over €550,000. If we can save a few tens of thousands of euros there, we will do it...

In the end, the decision between gas or an air-to-water heat pump depends on how one estimates the development of the price for gas or electricity. I personally would still install a gas boiler today, as I do not believe that the gas price will decouple that much from the electricity price over the lifetime of the technology. In 20 years, it might look different, who knows. Things look better with a significantly more efficient ground source heat pump. But that requires the appropriate property as well as the will and possibility for self-performance. Regarding the durability of the technology: I have an oil burner from 1982 in the basement, and it hasn’t given me any trouble since I moved into the house. Running costs are also reasonable; I spend less than 1000€ / year on hot water and heating. Of course, oil is currently very cheap, but even a 50% price increase wouldn’t really knock me off my feet. Of course, if the thing breaks down, something else will be installed, but as long as it runs, it is quite economical.