Which heating is recommended for KfW 55?

The gas condensing boiler itself is actually a bit cheaper than the air-to-water heat pump, but in combination with solar it definitely becomes expensive. Over 2,000 EUR is the material cost for just 2 collectors. Then there are expansion vessels, air vents, valves, and a lot of stuff around, as well as pipelines up to the roof. Also mounting systems for the solar on the roof, and then someone still has to install it on the roof.

If the air-to-water heat pump costs more than the gas condensing boiler plus solar, even significantly more, then the contractor wants to make a hefty profit. I would seriously consider whether I want to build with this company at all. They will surely calculate other surcharges similarly. Or maybe when he talks about the air-to-water heat pump he really means a high-priced model like Ochsner, but I don't assume that.

The surcharge is quite steep. Elsewhere you can already get a brine-water heat pump with a ground or trench collector or ground drilling. If possible, you can also have the heating removed and offered separately by a local heating installer. I think you can definitely save a few thousand euros that way. Apart from that, I assume that electricity prices will rise much faster in the next few years than gas prices. The federal government sees it exactly the other way around, which is why the air-water heat pump is also heavily promoted. But they probably just calculate using the producer price for electricity and ignore the constantly increasing Renewable Energy Act surcharge. Ultimately, when it comes to heating, you will hear as many different opinions as on almost no other topic in house construction. I would recommend listening to as many opinions as possible and then forming your own.

The air-water heat pump is being promoted because there is a long-term strategy for the energy transition. And this foresees that in the future not only households but also heating and mobility will run on electricity. Electricity can be stored relatively well. It can be transported easily, generated in many ways, with wind energy already having lower generation costs today than, for example, nuclear power. Without even taking into account the entire issue of nuclear waste disposal and so on.

The share of renewable energy keeps increasing, although it may still take decades until production is really mostly from renewable energy. But once that point is reached and we basically draw all our energy needs from electricity and thus from future renewable energy, then a sustainable cycle will be in place.

At that point it really doesn’t matter whether the train runs on nuclear or lignite today, or the tram, or the e-car, or the heat pump. It’s about the long-term concept of the energy transition.

I believe I already explained this in another thread: constantly rising electricity prices are rather unlikely and at some point they will even decrease. Generation costs have actually fallen but numerous fees and surcharges have been added. By the way, the same can be done with gas and oil at any time. The most important surcharge, the Renewable Energy Sources Act surcharge, will gradually decline after it has reached its peak (which is basically now). The Renewable Energy Sources Act mainly refers to old installations that feed in at 40-50 cents while electricity is only bought on the market for 3 cents. This gap is much smaller for new installations, fewer new installations are being built, and the old ones expire after 20 years.

In the long term, the government will develop measures to encourage gas and oil users to switch (i.e. tax on all types of fossil energy combustion). That may be in 2030 or later, but eventually there will still be heat pumps while oil and gas heating systems will no longer exist. Not because oil or gas will be gone, but because of the energy transition. If all current reserves are extracted and burned, it is known that the 2-degree target will be exceeded many times over. So the situation of running out of oil or gas will not occur.

One general contractor has now sent me a cost estimate that was created for other customers. The estimate comes directly from the building services company; the general contractor only wrote about 5% less here and there before presumably forwarding it.

The following three offers are included (price information is net unless otherwise stated, I have summarized the many individual items):

A)
- Gas condensing boiler with domestic hot water heat pump and decentralized ventilation (not sufficient for KfW55, plus 2400€ VAT)
- Buderus Logamax Plus GB 172 (2400€)
- Novelan domestic hot water heat pump (1770€)
- plus installation and materials (total so far 6500€)
- Underfloor heating, installation and accessories (3800€)
- Piping, installation and accessories (1700€)
- Sanha-Therm (no separate item listed for insulation layer)
- Radiators, installation and accessories (385€)
- 368€ (for one item it says 10lfm for "Hectu Plus pipe 25m each")
- in total, this amounts to approx. 15,000€ including VAT for the heating trade
- Zweotherm decentralized ventilation unit (2 pieces, each 460€)
- 2x Zewotherm exhaust system
- Electrical connection by the builder
- total approx. 1700€ including VAT for the ventilation (probably only living room/kitchen and exhaust in the bathroom)

B)
- Split heat pump with decentralized ventilation (achieves KfW55)
- Stiebel Eltron WPL 08 S Trend Set 5 (8000€)
- with integral storage tank HSBC 200l
- installation and core drilling etc.
- total so far 10,600€
- Electrical connection of the entire heating system by the builder
- Underfloor heating 2450€ (cheaper than A)
- Insulation layers of the underfloor heating by the builder
- Piping 1300€ (cheaper than A)
- Sanha-Therm (no separate item listed for insulation layer)
- Radiators 378€
- Ventilation as in A but with a second exhaust unit (1635€ net, more expensive than A)
- no note on builder's scope, possibly included in the term "entire heating system"?
- in total about 19,500€ including VAT

C)
- LWZ heat pump with central ventilation system (achieves KfW55)
- LWZ 504 (12,000€)
- plus accessories and installation
- Electrical connection of the entire heating system by the builder
- Total so far 14,300€
- Underfloor heating 3100€ (cheaper than A, more expensive than B)
- Insulation layers by the builder
- Piping 1300€
- Radiators 378€
- Ventilation pipes 5560€
- Zewotherm
- in total approx. 29,400€ including VAT

Total costs A: 15,000€ + 1700€ = 16,700€ (incl. VAT)
Total costs B: 19,500€ (incl. VAT)
Total costs C: 29,400€ (incl. VAT)
Difference A-B: approx. 3,000€ (incl. VAT)
Difference B-C: approx. 10,000€ (incl. VAT)

Total costs heating only net: 6500€ + 385€ = 6885€
Total costs air-water heat pump only net: 10,600€
Difference A-B: approx. 4,200€

Conclusion:

According to the offer, an air-water heat pump costs at least 4000€ more, although I have not yet figured out why the underfloor heating is cheaper with an air-water heat pump than with gas heating, maybe different heating circuits? Also, in B and C there are additional "insulation layers by the builder" as well as electrical connection of the devices. In A, however, the gas connection to the house still has to be offset (2500€?).

According to the offer from the general contractor to me, the air-water heat pump costs about 7000€ extra, which is a considerable surcharge. Considering the 5000€ bonus from the KfW bank, the air-water heat pump is therefore practically free as long as you organize the building services yourself.

B and C I consider comparable in content except for the ventilation technology. The ventilation system thus costs about 10,000€ + 1700€ (decentralized ventilation included in B) = 11,700€. According to the offer from the general contractor to me, the ventilation system alone costs about 8000€ extra (compared to nothing else, i.e., the price of the ventilation system would be equal to the surcharge). From this, I conclude that the combined unit LWZ has a surcharge of 3,700€ compared to the split variant; it has 35l more water volume and is presumably also overall larger dimensioned.

With B I see handwritten notes under the final amount as well as a surcharge of 5%; this should be the share of the general contractor. Thus, the above-mentioned prices initially come 1:1 from the building services company.

I am somewhat shocked by the high costs of the gas condensing boiler or the whole costs around it (I'm not even referring to the underfloor heating). However, this gas condensing boiler does not include a solar system; if it did, I agree with Grym's statement that an air-water heat pump should be roughly cost-neutral compared to gas condensing boiler + solar thermal.

I consider the price of the ventilation system of almost 12,000€ to be far too high, especially since the general contractor already offered it for 8000€.

If anyone is interested in the document sent to me, just send me an email via private message.

For the LWZ504 there should also be a €1500 subsidy from the BAFA.