What to replace an oil heater from 1989 with in an old witch's house?

Wrapping the house in plastic

Wrapping the house itself is actually good. It also fits with the heat pump – I am currently renovating to KFW 55, including an apartment with a heat pump. For that, I need a flow temperature of 40 degrees for the radiators. And you first have to be able to place 33 cm radiators. Without insulation, it wouldn't have been possible or only with a significantly higher flow temperature and then a poorly performing heat pump.

I think it might make sense to bring in an energy consultant for our project,

They are not expensive, are subsidized, and pay off!

Hmm we already have some 33cm insulation boards which could partly still be doubled without problems, because they are only 30cm high.

I am not such a fan of the insulation craze; in our apartment, for example, the old beautiful wooden windows were replaced by modern plastic windows. When we came back from vacation there was mold on the wall, because we obviously didn’t ventilate while we were away. With the wooden windows before, there was never a problem because they always provided some air exchange. The mold removal/painting cost more money than could be saved on heating costs over the next 10 years. Not to mention the installation costs of the windows. A low-energy house certainly makes sense in my eyes, but the overall concept including the ventilation concept must be right. In my opinion, you will never turn an old farmhouse into a low-energy house.

The father of a friend has a construction company and he advised me against insulation; they replaced insulation this year in several houses that wasn’t even 8 years old. We also have a neighbor who insulated his house, and since the woodpeckers took a liking to the insulation, he’s not so happy about the woodpeckers in the garden anymore.

Pessimistic Back-of-the-Envelope Calculation

I’m assuming a cold winter with 2400 liters of heating oil consumption. Rounded, heating oil has a heating value of 10 kWh per liter, so 24,000 kWh heating demand.

If I understood correctly, I should multiply this by the efficiency of the heating system? And would roughly get 24,000 kWh * 0.85 efficiency = 20,400 kWh?

Now I assume my heat pump only achieves an annual performance factor of 2.4 (the worst heat pump in the Fraunhofer study managed 2.6, but almost all of them had underfloor heating).

So I would need 24,000 / 2.4 = 10,000 kWh of electricity to heat the house. I pay about 25 cents per kWh for electricity (currently less). The result would then be 2,500 euros of heating electricity costs per year, quite a substantial amount at first. Is the calculation correct so far?

However, I think there are several ways to reduce this amount:
* achieve a better annual performance factor than 2.4
* heat with a wood stove on cold days and enjoy the fire
* generate electricity especially in the transitional seasons with a solar system and supply it to the heating system
* milder winters due to climate change (even with the old uninsulated roof, we often came well below 2400 liters)
* consider the efficiency of the current heating system in the calculation?

In contrast, 2400 liters of heating oil today would cost around 1400 euros, but due to the 2000-liter tank, we would have to pay for two deliveries. A modern condensing boiler would definitely reduce consumption somewhat. However, I believe that even with a condensing boiler, the maintenance costs would be somewhat higher than with a heat pump?

On the plus side for the heat pump:
* no more stress with heating oil in the future
* space gain in the basement (although the space is not currently needed)
* legal certainty, my heating will not be banned anytime soon
* wood stove in the living room (warm your feet by the fire after kitesurfing!)
* replacing the heating every 15-20 years is cheaper than with oil
* hopefully a less climate-damaging heating system

What the above calculation does not yet take into account are the acquisition costs.
I would roughly estimate 15,000 euros for replacing the oil burner and repairs. The same for switching to a heat pump.

The latter, however, is heavily subsidized, so the additional heating costs compared to oil would likely be covered by the savings within several winters. In addition, the heat pump makes it possible to pursue further optimization measures on the house (e.g., better windows/photovoltaic system) with increased funding?

Am I sugarcoating this? Where is my flaw in thinking?

What about the roof? Can't you just insulate it with EL? That should save about 10-15%.

The roof was completely rebuilt and modernly insulated after a hailstorm destroyed the old roof, but there are no experience values regarding consumption yet, as this is our first winter with it. The effect of the insulation inside the house is clearly noticeable. Under the sloping roof, it is now much warmer.

The attic conversion was done in such a way that I can eventually tear out the attic to gain ceiling height on the upper floor.

The roof was completely rebuilt and insulated in a contemporary manner after a hailstorm destroyed the old roof, but we still lack experience regarding consumption since this is our first winter with it. The effect of the insulation is clearly noticeable in the house. Under the pitched roof sections, it is now much warmer.

The attic conversion was done in such a way that I can eventually tear out the attic to gain ceiling height on the upper floor.

That sounds good. I think replacing the oil heating system should cost less than 10k. As of now, you would be about 900€/a more expensive with a heat pump. If you subtract the chimney sweep and maintenance costs, you might be looking at around 700€. With that, you could first fix small issues. For example, air leaks around the windows, etc., unless that has already been done. I don’t have that in mind. Since experience values are missing, just wait for the winter first and reduce the flow temperature to an absolute minimum. The lower, the better for the heat pump. Possibly also replace or supplement radiators.