Renewal of heating system in old building, which system?

At 30 years, I would rather estimate an efficiency of around 70-75%

I didn't calculate it, but I wouldn't rely on the heating support. The system also has to be configured and adjusted almost perfectly there. My honest opinion: just have the smallest gas condensing boiler installed and that's it. Then carry out a thermal balance in the first year and be happy with the low costs.

And I say this as a heat pump fan

Yes, I also calculated the heating demand to be about 23-24,000 kWh. The oil heating is certainly not optimally adjusted. That's why I was so surprised that the heating company calculated with a heating load of 11,000 kWh.

Great, thanks again for the tips. I would only have the heating support (solar thermal) installed because then I would receive 40% BAFA funding on all eligible costs. Since I am planning several measures, I thought it might be worthwhile to basically get the heating support for free. Because if I commission the planned measures (gas condensing boiler, oil boiler removal, oil tank removal, gas connection, radiator replacement) without funding, I actually come to the same or slightly higher costs than with a solar system on the roof. But that's strange.

What do you think?

Best regards

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My honest opinion: just have the smallest gas condensing boiler installed and that's it. Then carry out a hydraulic balancing in the first year and be satisfied with the low costs.
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Because you wrote smallest gas condensing boiler. One company wants to install a hybrid system with a gas condensing boiler with 24 kW. Is this gas condensing boiler too large for 200 m2 of living space and about 240 m3 heated space? Cost point 4200 EUR.

Additionally solar thermal with vacuum tube collectors heat pipe, complete rooftop set 8.24 m² with 50 power tubes. Allegedly, solar systems with tube collectors are much more efficient than flat plate collectors? Cost point about 10,000 EUR.

And hot water preparation with 600 liter buffer tank. Cost point about 2,000 EUR.

Total costs including all additional services, such as gas connection, removal of old oil tank, re-equipping heating room with heating circuits, etc., about 33,000 EUR gross before subsidies) and 21,500 gross (after subsidies).

If I now subtract all items for the solar thermal and do not receive 40% subsidy from BAFA, then I pay about 24,000 EUR gross.

So you recommend I possibly have a very small gas condensing boiler installed with, for example, a 200 L - 300 L storage tank?
What gross costs should I roughly expect?

Thanks.

Best regards

The most important thing is the lowest heating output; the heating system should be able to modulate as far down as possible.

The smallest heating capacity is important; the heating system should be able to modulate down as far as possible.

The gas condensing boiler offer indicates a power range of 3.4 kW to 24 kW. Is that what is meant?

I have now asked the heating company that provided the heat pump offer again. They said that the heating load of 11 kW was calculated based on the oil consumption of 2,500 liters and data about the building (year of construction, insulation standard, etc.).
The annual performance factor of 3.9 is indeed realistic when calculated at 55 degrees flow temperature.
Is there anyone here who has also installed an air-water heat pump in a similar existing property?

Best regards

How about a small heat pump for the ground floor and still oil for the upper floor? I will now implement it that way because in my house the upper floor apartment is rented out and therefore no underfloor heating can be installed there. This way I can operate a flow temperature of max. 30 degrees. If the upper floor is ever vacated, simply add a second small heat pump for the upper floor (or a larger version for both units). Who uses the apartment and how?