Different statements from Gu / Gü about the topic of heating

That’s what I primarily meant. Technical skill and understanding, no super tiny plot, 2-3 helpers and an excavator on an hourly basis. Then geothermal energy works very cheaply. I personally implemented it myself and it works in one weekend.

I find #3 very helpful! Some remarks:

Since the questioner is talking to two companies, I assume he is the landowner. He is thus in the fortunate position to have free choice. He decides which technology he uses. After that, he looks for the appropriate craftsman. Not the other way around, first the contractor, then the technology.

There are, roughly speaking:
- Gas condensing boilers
- Air-to-water heat pumps
- Geothermal heat pumps (either as deep drilling or as trench collectors)
- Groundwater heat pumps
- Exhaust air heat pumps
- Pellet heating systems
- District heating
- Combined heat and power plants
- ...

In any case, I see (as already said) a low-temperature underfloor heating system as the basis! Besides that, the system should be designed for the water demand (showers, etc.).

In addition to investment and operating costs, legal requirements play a role, keyword Energy Saving Ordinance and Renewable Energies Heat Act. That means the heating system is related to measures such as solar thermal, controlled ventilation with heat recovery, insulation of the building envelope, quality of windows, etc. And not only through technical dependencies (insulation – energy demand) but also through regulatory conditions. Possibly, KfW requirements will also apply.

In these matters, the chosen heating installer does not help, but the architect or better the energy consultant!

By the way, own work can be included everywhere (e.g., laying the heating loops). In my opinion, trench collectors are often brought into play because without own work they quickly become very expensive.

So it means: underfloor heating with gas or air-water heat pump

So it means: underfloor heating with gas or air-to-water heat pump

Yes and no:
- Underfloor heating – in all variants can be implemented with the system temperatures mentioned above (30/26/21)
- Gas condensing boiler must be combined with a renewable source to comply with the energy saving ordinance. Solar thermal for domestic hot water is often sold here because it is usually the cheapest option. However, in your case, I would have an energy consultant calculate photovoltaics or ventilation with heat recovery as an alternative.

- Air-to-water heat pump: After gas, the next cheapest option, but requires absolutely appropriate design of heating surfaces and correct sizing of the heat pump. Google "There is no fire burning in the heat pump." Unfortunately, very few heating installers have internalized this. Also, please pay attention to noise emissions, distances to bedrooms & neighbors!

- Geothermal: Actually the "best" option, but financially usually the most expensive due to high costs for deep drilling. If interested and skilled, building a trench collector yourself is also optimal in terms of cost.

The disadvantage of the [Grabenkollektor] is its space requirement and the associated usage restrictions. For 450 m² plots, that would be a dealbreaker for me. For 1500 m² park areas, it’s not an issue if planned well.

why should a trench collector be ruled out for 450m²? What kind of usage restriction do you mean? Or the other way around... feel free to google ring trench collector and read a bit in the forum you come across... several collectors of such sizes have already been implemented there.