The matter with heating - air/air, air/water, or gas?

Wood, stone, concrete?

Wall construction?

Primary energy demand?

In my opinion, if you do not build well below the KFW-70 requirements, then gas offers the best price/performance ratio in our regions...

We also have a KfW-70 house and saved the approximately 10TSD additional cost of a heat pump and can now heat for a while with it...

In my opinion, most people are best advised to use gas. There are now providers who cannot live with gas for their concept" (primary energy demand often does not fit the fancy KFW 0815 label). Here, an air-to-water heat pump might also be okay. Adding photovoltaics does make some sense. However, investment costs are somewhat higher than with gas + small ST – operating costs are about the same (of course, it depends on the size of the photovoltaics). There are also concepts for the LLWP. The air-to-air heat pump is a solution with relatively low investment costs in the right house. The solutions become more robust against planning errors from bottom to top. Regarding your points that you raise:

[*]Low operating costs come at the price of high investment costs. [*]The possibility to install "modern" (= low flow temperatures?) heating systems with underfloor heating also exists with gas – nothing prevents you from using small pipe spacings and low flow temperatures. However, the "most modern" type of heating system is the air-to-air heat pump – which currently does not require underfloor heating ;-) [*]I cannot say anything about living comfort, as I have never lived in a house with ventilation heating (at least not in one that was not excessively poorly insulated).

I agree with my predecessors: A bit more input on the construction method and the targeted KFW standard would be great.;)

We heat with gas. Our underfloor heating was installed in as tight loops as possible so that we might be able to use a different heating system later. However, we had long considered a brine-water heat pump.
Because we did not invest in the brine-water heat pump, we will be able to heat with gas for a very, very long time. ;)

The choice of heating system is connected with a good gut feeling and personal preferences.

Wood, stone, concrete?

Wall construction?

Primary energy demand?

In my opinion, if you don’t build far below the KfW-70 requirements, then gas offers the best price/performance ratio in our regions...

We also have a KfW-70 house and saved about 10k extra compared to a heat pump and can now heat for a while with that...

I cannot understand the figure of 10k € surcharge.
An air-water heat pump device (with a 200l water tank) costs around 10k euros (about 5-9 kW power), but a condensing boiler (without water storage) also easily costs at least 2k if you use a branded device; in addition, maybe another 1k (?) minimum for intake/exhaust air extra costs (you can specify more precisely what that costs, or others can, I no longer have gas).
Then there are the gas connection costs, which vary greatly depending on the city, but overall you will probably lose another >1k euros.
If you do not yet have a controlled residential ventilation system with heat recovery planned, or want to build beyond the Energy Saving Ordinance, you quickly need solar thermal, which also costs quite a bit.
Overall, the savings when building are therefore limited. Heating with gas is of course also not cheaper than with the air-water heat pump.
So you shouldn’t decide based on finances but based on the situation: the most important point "is there even gas" (with us the plot was offered/sold "with gas", during development (after purchase!) the utility said it’s not worth it, there is no gas - I would have liked to cook with it), then of course ideology (do you want "fire," do you prefer only "renewables" and take the air-water heat pump and only buy "green" electricity etc. pp), what does the space/environment look like, where are you building (please no air-water heat pump high up in the Alps), and so on.

The thing with the GÜ's and their surcharges no one can explain... a price is simply quoted and then there is little to nothing you can do except accept or leave it.

For us, the difference between a gas boiler with solar thermal and an air-water heat pump was 10,000.

So about 1,500 more invested in the gas connection and that’s it... thus saving almost 10,000.

The controlled residential ventilation was also supposed to cost 12-14,000... in the end, one was installed for half the price through an external ventilation company, which we hired ourselves.

If the heating system is properly planned and executed, then there is actually very little that can go wrong with the heating. The potential savings on heating costs in new buildings is now very low. We're talking about 100 or 200 euros per year! That should hardly make a difference for anyone who can afford a house. In other words, you can fully focus on your existing conditions when choosing the heating system.

If the BT or Gü offers an air-water heat pump, then it will fit the concept, so just take it and that's that. If they prefer gas, then they probably have good experience with it, so that fits as well. If you don't go for an off-the-shelf solution, you look at the conditions: basement yes/no, gas connection available, pellet storage possible, noise at the installation location critical, Kfw requirements etc., and then choose a suitable system.

In short, the economic factor in consumption costs is your least problem ;-)