ᐅ Which heating system is best for a household of 2 people, later expanding to 4?

I’m not a fan of “a bit of everything” either, but especially with a KfW40 house, which is already at the lower end of the energy consumption scale and close to energy self-sufficiency, a sensible combination makes sense. If you strictly decide based on cost-benefit analysis, you won’t be able to justify solar thermal systems or a battery storage for the photovoltaic system.

In the long run, the type of heating system doesn’t significantly affect heating costs. However, no one can predict the future prices of electricity, gas, pellets, or oil. Therefore, a level of self-sufficiency is the easiest way to become independent from these fluctuations. And it doesn’t require that many elements to achieve this.

Based on your description, a underfloor heating system is installed, correct? Many prefab home builders often recommend an air-to-water heat pump, which I am somewhat skeptical about. I also believe that in your case, an air-to-water heat pump or preferably a ground-source heat pump using horizontal ground collectors or deep drilling would be more appropriate. Solar thermal systems are probably less effective; photovoltaic panels might be better, but those can also be added later if needed.

With good heating system planning, you might be able to use a ground-source heat pump without a buffer tank and expansion vessel, which would save costs. Combined with the BAFA subsidy, this could make the setup quite financially attractive.

Yes, exactly. The decision is basically between a KfW 40 Plus house with a photovoltaic system of about 5 kW, including a buffer tank and an air-to-water heat pump, or just an air-to-water heat pump without the photovoltaic system and buffer tank.

Someone also tried to persuade us to use an air-to-air heat pump, but I think that can be disregarded. Underfloor heating works better with the air-to-water system, or am I wrong?

The question is simply whether it will ever pay off, but we were told it probably won’t. After about 20 years, the solar panels will likely need to be disposed of, which will cost a lot of money. The batteries will also have to be replaced, so the "Plus" option might even be more expensive—even with subsidies.

But as I said, I’m personally still undecided whether to go with or without it.

Before starting our construction project, I requested a quote for a 6 kWp photovoltaic system and found that, including battery storage, the payback period was just under 20 years (which roughly corresponds to the lifespan of the components, with the battery possibly being shorter). Without storage, the payback period was about 10 years. The increased self-consumption through energy storage currently does not justify the additional costs given the current battery prices.

The situation changes, of course, if the battery storage is partly funded through the KfW40+ repayment subsidy and possibly Program 275 (I’m not sure if they can be combined). In that case, a large portion of the costs is covered, and the system pays off faster.

If you decide in principle to go with photovoltaics (with or without a battery), a heat pump is the obvious choice for the heating system. I do not consider using air as the heat transfer medium inside the house to be practical, so an air-to-air heat pump is out. Among the other options, the efficiency of a ground-source (brine) or water-source heat pump is higher than that of an air-to-water heat pump. The installation costs for the heat source are €0 for an air-to-water heat pump, between €2,500 and €10,000 for ground-source systems depending on the setup, and likely highest for water-source systems, which also come with the most regulatory requirements.

Thank you all for the help!!!! I will probably go with an air-to-water heat pump with photovoltaic preparation now, and possibly retrofit everything later if batteries become cheaper...