Which heating system is currently the best?

By secure I mean without negative surprises regarding consumption costs.

I don't quite understand your statement. Everyone says that you shouldn't operate uninsulated houses with an air heat pump because these pumps are supposed to be overwhelmed then.

I just see you are writing: Erdwärmepumpe

One thing upfront: I am also just an amateur.

I just wanted to clarify that your generalization between gas condensing boilers and air-to-water heat pumps cannot be correct as is.

I simply based it on fixed costs and variable costs of different heating types.
To show the extremes, I used gas condensing boilers and geothermal heat pumps on the heating side and super-insulated and uninsulated on the house side.

The air-to-water heat pump you mentioned should be somewhere between gas condensing boilers and geothermal heat pumps in both fixed and variable costs. Where this type of heating finds its optimum must be calculated. You cannot generalize that.
Furthermore, the heating type changes the KFW rating, not the other way around.

....The higher the heat demand of a house, the greater the share of variable costs (costs for energy sources) in the total costs. The lower the heat demand of the house, the smaller the fixed costs (maintenance, acquisition, interest) of the heating system should be.

Correct. However, overall I would phrase it differently: The higher the demand for heating and hot water, the higher the requirements for energy efficiency. Therefore, in order to find the right solution overall, a fundamental assessment (actual demand (capacity, energy) for heating and hot water) must be carried out.

....High fixed costs and low variable costs = e.g. geothermal heat pump low fixed costs and high consumption costs = e.g. gas condensing boiler

That is generally not correct!

....So it makes no sense to install a super expensive heating system with minimal consumption in a "passive house". Here, the gas heating could certainly be the cheaper alternative. The only question is whether the title "passive house" then remains.

Correct, because the sum of the burdens is equal. You can build a PH very cheaply if you forgo certification. However, if you are exclusively aiming at grant incentives, there is no way around it.

....In an uninsulated old building, on the other hand, a heating system with high fixed costs and low consumption (e.g. geothermal heat pump) would be the better alternative.

Correct! However, in existing buildings there are limiting conditions (heating surfaces, hydraulics) that make the use of ground-source heat pumps and especially air-source heat pumps nonsensical. Of course, the manufacturers’ promotional hype does not address this. Thus, one finds "heat pumps suitable for old buildings," "heat pumps with flow temperatures up to 60°C and higher," etc. Many have fallen for this and must live with high consumption costs despite the relatively high investment (capital costs). Those who rely exclusively on the seller or craftsman here are indeed abandoned in the end. An exact fundamental assessment has of course been "saved" in these cases.

Best regards

NB: There is no ultimate heating system, as the specific boundary conditions differ significantly.

Unfortunately, the last winters were a bit colder and thus the air heat pump became less efficient, which the air heat pump manufacturers probably did not expect (because of global warming).

"Global" warming does not mean that it gets warmer everywhere. In northern Germany, for example, it is getting colder. But that's just by the way. A blanket denial of the question about the best heating system, as some do, I consider to be just as wrong as giving a blanket answer to it. Many factors have to be taken into account, such as the orientation and slope of the roof, soil conditions, climate zone, sunshine duration, average temperatures, etc. These are all external influences. Once these are defined, one can certainly find the best solution for a single-family house (my opinion, as mentioned). As long as it is about independence and not about costs, I see the answer to the question of the best heating system in a solar thermal system. A very large collector area for the solar system, preferably also photovoltaics to produce some electricity for oneself (I do not consider feeding in the grid to be useful), and a very large tank. How big depends entirely on the building size. I don't want to write a novel now, but with any other system I would now clearly see disadvantages in terms of dependency. Of course, you depend on the sun with solar, but it is not an energy corporation.

Hello everyone,

I just wanted to speak up again, thanks again for the many posts and information. I really appreciate it. Although I still can't really decide. But that's also because the final construction method has not yet been clarified. And as far as I understand, first clarify the construction method, then have the actual demand/consumption checked, and after that comes the selection of the heating system.

The idea of a solar thermal system + a bit of photovoltaics in combination with a controlled residential ventilation + heat recovery is currently the best option in my opinion.