Which heating? Gas or electric heating?

Please think very soberly. Geothermal energy works. But the FHZ must be designed for low flow temperature, tight coils, and the house must be well to top insulated. Does this apply to your old building? If in doubt, do not hesitate and order gas. k.

Please think very soberly. Geothermal energy works. But the FHZ must be designed for low flow temperature, tight coils, and the house must be well to top insulated. Does this apply to your old building? If in doubt, do not hesitate and order gas. k.

I am not a professional, but I believe you can hardly speak of insulation with normal Poroton bricks, can you? The flow temperature is definitely very low at the moment. I do not know the definition of tight coils in the FHZ, but on the plan it looks more like a generous layout....

It all rather speaks for a proper gas heating system...

Yes.

The question also concerns me. We want to renovate a house, so bring it up to date. My plan would be a heat pump. However, the civil engineer said that gas should additionally be planned for support. We have not clarified any details yet, so I am curious about the explanation. But for me, it is also the case that I do not want to be dependent on a fuel.

Either or! Both at the same time is wasted money. In existing buildings, heat pumps are rarely worthwhile. With a heat pump, you are not directly dependent on gas, but if at some point no more gas comes from the pipeline, there won’t be enough electricity either. You always need something to heat. If you want to be independent and self-sufficient, build a passive house with proper photovoltaics, a garden for self-supply, a chicken coop, and buy yourself a good bicycle.

But I also feel that I don't want to be dependent on a single fuel.

Better on one than on both. You don't want to combine the disadvantages of a heat pump with the disadvantages of gas. Don't agree to anything, no matter what clever justification comes.