ᐅ Replacing the Heating System in an Older Home: Which Option Is Best?

tiborb schrieb:

Yes, somehow a system error :-O But what kind?

Your house doesn’t match the heat pump, and the oil heating is effective. As I said, the rest should be calculated by professionals.

So, I have researched again and calculated the different options:

Current situation: Oil heating with low-temperature boiler
With an oil consumption of 2,500 liters and approximately 11.4 kWh/liter heating value for oil, this converts to around 27,500 kWh/year.
Given the (fluctuating) oil prices, the current annual cost is about 1,150 EUR, which could rise to around 2,250 EUR if prices increase to 0.90 EUR/liter. The average is approximately 1,700 EUR per year.

Air-source heat pump
If we use the offered air-source heat pump with a calculated seasonal performance factor (SPF) of 3.9, then for a calculated heating load of 11 kW, the annual electricity consumption would be about 5,641 kWh/year. At an average electricity tariff of 0.30 EUR/kWh, this equates to approximately 1,700 EUR per year.
If the air-source heat pump turns out to be less efficient than calculated and only achieves an SPF of around 2.5, the annual electricity consumption would be about 8,800 kWh/year for the same heating load. This results in annual costs of approximately 2,640 EUR per year, or 220 EUR per month.

Gas condensing boiler hybrid with solar thermal system (8.5 sqm (91 sq ft))
If we switch to a modern gas condensing system, we would likely consume around 23,000 kWh/year of gas. With current gas tariffs, this corresponds to annual costs of approximately 1,060 EUR.
If a solar thermal system of around 8.5 sqm on the roof were added, providing about 15% heating support (theoretically up to 25%), this could save around 3,450 kWh/year through solar energy. That means about 19,550 kWh/year and approximately 900 EUR per year, or 75 EUR per month.

Conclusion
For the house described – see https://www.hausbau-forum.de/threads/Erneuerung-Heizungsanlage-im-Altbau-welches-System.34791/#post-399934 – the gas hybrid system with solar thermal would actually be the most economical option, especially if a replacement is planned under the BAFA subsidy program with 40% cost coverage.

It is important to know that we also want to remove the oil heating system, as it is over 30 years old, and we want to use the oil tank room as living space. The gas connection, after discussing with the local utility company, costs approximately 2,000 EUR gross, but effectively only 1,200 EUR due to eligibility for subsidies.

In my opinion, the high investment in the solar thermal system of around 9,000 EUR gross is still worthwhile within the framework of the 40% subsidy. Annual gas cost savings of approximately 233 EUR multiplied by a 25-year lifespan equals 5,825 EUR, plus 9,800 EUR BAFA subsidy for the gas heating components, oil tank removal, gas house connection, radiator replacement, etc., (total gross costs 24,500 EUR) can be saved.
Am I calculating this correctly, or have I made a mistake in reasoning?

Maybe a professional could take a look.

Thank you.

Best regards

As I mentioned earlier and you also calculated yourself, your house currently requires about 27,500 kWh.

You need to divide this number by the annual performance factor to determine your electricity consumption. With a factor of 3.9, you don’t get 5,641 kWh but close to 7,000 kWh.

The heat demand of your house doesn’t change simply because you use a different heat generator.

Even with a condensing boiler, you still need 27,500 kWh.

I haven't done the calculations, but I wouldn’t rely on the heating support. The system needs to be almost perfectly configured and adjusted for that to work. My honest opinion: just install the smallest gas condensing boiler and be done with it. Then perform a hydraulic balancing in the first year and be satisfied with the low costs. And I say this as a heat pump fan.

T_im_Norden schrieb:

As I mentioned before and as you also recalculated yourself, your house currently requires about 27,500 kWh.

You need to divide this number by the annual performance factor to get your electricity consumption.
With a factor of 3.9, you don’t get 5,641 kWh but almost 7,000 kWh.

It probably won’t be exactly like that. I think you can expect around 20–22 MWh. The 30-year-old oil boiler won’t be efficient and is likely set incorrectly.

If you assume the approximately 10 - 15% savings that a condensing boiler can provide, that roughly matches.

That would be around 23,000.

However, since you can’t tell from a distance how efficient it was, I always assume the worst-case scenario. Especially since triple glazing is already installed here and partial insulation has been done.