Hybrid heating: Is a heat pump with a gas condensing boiler sensible in old buildings?

The (room-specific) heating load should be determined by a good energy consultant, or even better, by an engineering firm. It will definitely not be more than 10 kW. And then you don’t use gas anymore. You can’t get any contracts anyway, and next winter possibly no gas even with a contract.

Install a 10 kW monoblock heat pump and that’s it. Or better yet, insulate first and install a smaller heat pump. If retrofitting underfloor heating is an option, I would equip everything with it if possible. That saves the heating buffer and mixer and really lowers the flow temperature. If that’s not possible everywhere, wall or ceiling heating is also possible. The main thing is to activate large surfaces.

Then install as much photovoltaic as roof areas are available and you are prepared for the future.

The (room-by-room) heating load should be determined by a good energy consultant, or even better, by an engineering firm. It will definitely not be more than 10 kW. And then you don’t use gas anymore. You can’t even get contracts, and next winter possibly no gas even with a contract. Install a 10 kW monoblock heat pump and that’s that. Or even better, insulate beforehand and use a smaller heat pump. If retrofitting underfloor heating is an option, I would equip everything with it if possible. That saves the heating buffer and mixer and really lowers the flow temperature. If that’s not possible everywhere, wall or ceiling heating is also possible. The main thing is to activate large surfaces. Then add as much photovoltaics as roof areas are available and you are prepared for the future.

Ok, thanks. Yes, I just thought because the house is already older. From the year 1972. And the living area is 142 sqm. But I suspect the heating engineer wants to sell gas specially because he can cash in on maintenance work over time. However, I have to say that some insulation measures have been done by the previous owner, for example the 10 cm wool in the top floor ceiling. The windows currently still have insulating glass but will be replaced by double glazing, or possibly triple glazing if the facade is still insulated after all. I have just heard everywhere that heat pumps only pay off in new buildings or if everything is excessively insulated – according to the latest standards etc.

I have only heard everywhere that heat pumps are only worthwhile in new buildings or if everything is excessively insulated - according to the latest standards, etc.

That is definitely wrong. Next to me, you will find plenty of people here who prove the opposite. And completely independent of the "worthwhileness," virtually all houses must be converted to heat pumps within the next 20 years. Unfortunately, there are no other options for the necessary CO2 neutrality by then. From an ecological perspective, it would therefore be disastrous to install anything else now. Very likely economically as well.

From an ecological standpoint, it would therefore be fatal to install something else now. Economically very likely as well.

I disagree with you on both points. With a high heating load and high flow temperature, the efficiency of a heat pump is simply poor. Consequently, a lot of very expensive electricity is wasted, which will still mainly come from coal and gas in winter in 10-15 years. So neither ecologically nor economically.

Although politics is currently telling a different story, it will come face to face with reality in a harsh way. Starting with the shortage of installers for heat pumps, craftsmen for the necessary core renovations, missing power lines, etc.

... electricity that will still mainly come from coal and gas in winter even in 10-15 years. So neither ecological nor economical.

People who know more than all of us together see it completely differently. @TE I initially assumed the heating load as given, my mistake. Where does it come from, it is very high considering that everything except the facade fits and the house is of normal size? This is crucial for the decision.

People who know more than all of us together see that quite differently.

Predictions are difficult, especially when they concern the future ;)
So I simply approach the matter freely according to Taleb and Occam with as few assumptions as possible. In winter, the sun shines little and is low, so photovoltaic is to be forgotten. In addition, we often lie under fog here in the south and sometimes there is no sunlight for 2 weeks in winter. Sometimes there is wind, but often as a storm and also bad. So the electricity would have to come from the windy north, but the lines there have to struggle with a citizen initiative in every second village. Wind turbines as well, by the way. What else remains?
We are currently shutting down nuclear power, hydropower is considered "renewable" but today you no longer get approval to flood an alpine valley in an environmentally friendly way. German geography doesn't offer much anyway, even if you wanted to.
Basically, you also have the problem that you have to massively oversize unreliable energy generation like sun and wind (expensive and not exactly ecological) so that it is sufficient even in unfavorable cases. Even with storage on the grid level (also expensive).

In the end, only coal, gas, and buying electricity from neighbors remains. Everything else expects miracle technology. Expert opinions are nice and all, but healthy doubt is also important.