Which heating system should be installed in a household with 2 and later 4 people?

I am also not a fan of "a bit of everything," but especially with a KfW40 house, which is already at the lower end of the energy consumption scale and autonomy is within reach, I consider a sensible combination appropriate. If you decide purely based on cost/benefit, you will not be able to justify solar thermal or a storage system for the photovoltaic system. In the long run, it does not matter what type of heating you have for heating costs. However, no one can predict the development of electricity, gas, pellets, and oil prices. Therefore, a certain degree of autonomy is the easiest way to become independent of that. And it does not require that many elements for it again.

According to your description, underfloor heating is installed, right? Many prefabricated house builders like to sell a [LLWP] again and again, which I think less of. I also think that in your case an air-water heat pump or directly a ground-source heat pump with trench collector or deep drilling would be more sensible. Solar thermal is probably less useful; if anything, photovoltaics, but that can possibly also be added later. With good heating planning, you might be able to manage without a buffer tank and [ERR] with a ground-source heat pump, which in turn saves costs and, together with the BAFA bonus, would be relatively lucrative.

Yes exactly, the decision is actually between a Kfw 40 plus house, that is with a photovoltaic system of around 5 KW with a buffer storage and air-to-water heat pump, or just an air-to-water heat pump without a photovoltaic system and buffer storage. Someone also wanted to sell us an air-to-air heat pump, but I think that can be ruled out, since floor heating is already better with that, or am I wrong there as well? The question is simply whether it would pay off eventually, but probably not, we were told by someone, because the solar panels will probably have to be disposed of after about 20 years and that will cost a lot of money, likewise replacing the batteries, and therefore the "plus" would probably even be more expensive... even with subsidies. But as I said, I myself am so undecided whether with or without?????

Before the start of our construction project, I had a 6kWp photovoltaic system quoted and came to a payback period of just under 20 years with storage (which is about the lifespan of the components, possibly shorter for the battery) and about 10 years without storage. The higher self-consumption through electricity storage therefore does not justify the additional costs (with the current battery prices). It looks different, of course, if the storage is co-financed through the KfW40+ repayment grant and possibly Program 275 (no idea if that is combinable). Then a large part of the costs is covered and the whole thing pays off correspondingly faster. So if you basically decide for photovoltaics (whether with or without battery), a heat pump suggests itself as a heating system. I do not consider using air as a heat carrier in the house to be useful, so the air-to-air heat pump is ruled out. Among the other options, the efficiency of a brine or water heat pump is higher than that of an air-to-water heat pump. The development costs for the heat generator are €0 for the air-to-water heat pump, between €2,500 and €10,000 for brine depending on the system, and probably highest for water and associated with the greatest requirements.

Thank you all for the help!!!! I will probably choose an air-water heat pump with [Photovoltaik Vorbereitung] now and possibly convert everything if batteries become cheaper...