ᐅ Which type of heating system is recommended for a KfW 55 energy-efficient house?

The gas condensing boiler itself is actually somewhat less expensive than the air-to-water heat pump, but combined with solar, it definitely becomes costly. Just the material cost for two collectors exceeds 2,000 EUR. Then you have expansion tanks, air vents, valves, and a lot of other components, as well as piping all the way up to the roof. Additionally, there are mounting systems for the solar panels on the roof, and of course someone has to install it up there.

If the air-to-water heat pump costs significantly more than the gas condensing boiler plus solar, then the contractor is likely aiming for a considerable profit. I would seriously reconsider whether I want to build with this company at all. They will probably charge similarly high markups on other items as well. Or maybe when referring to the air-to-water heat pump, they are talking about a premium model, but I don’t think that’s the case.

The additional cost is quite significant. Elsewhere, you can find a brine-to-water heat pump with a ground or trench collector or geothermal drilling.

If possible, you could also leave out the heating system and have it installed separately by a local heating specialist. I think you could definitely save a few thousand euros this way.

Apart from that, I expect electricity prices to rise much faster in the coming years than gas prices. The government sees it the other way around, which is why air-to-water heat pumps are being heavily promoted. But they probably only consider the wholesale price of electricity and ignore the continuously increasing surcharge under the Renewable Energy Act.

In the end, you will hear more diverse opinions about heating than on almost any other topic in house construction. I would recommend listening to as many viewpoints as possible before forming your own opinion.

The air-to-water heat pump is being promoted because there is a long-term strategy for the energy transition. This strategy envisions that in the future, not only households but also heating and mobility will run on electricity. Electricity can be stored relatively well and transported easily. It can be generated in many ways, with wind energy already having lower production costs than, for example, nuclear power. This doesn't even take into account the costs and issues related to nuclear waste storage.

The share of renewable energy continues to increase, although it may take decades before production is mostly based on renewable sources. However, once that point is reached and we meet all our energy needs with electricity—thus from renewable energy in the future—a sustainable cycle will be in place.

At that point, it will not really matter whether trains currently run on nuclear or lignite coal, or whether trams, electric cars, or heat pumps are used. The focus is on the long-term concept of the energy transition.

I believe I mentioned this in another thread: constantly rising electricity prices are unlikely, and eventually, prices may even decrease. Production costs have actually fallen, but numerous fees and surcharges have been added. Similar measures could be applied to gas and oil at any time. The most important surcharge, the Renewable Energy Act surcharge, will gradually decrease after reaching its peak (which we are approximately at now). This act mainly supports older installations that feed electricity into the grid at 40 to 50 cents but are only paid around 3 cents on the market. This gap is much smaller for new installations, fewer new systems are being built, and the old plants are reaching the end of their 20-year operational life.

In the long term, the government will develop measures to encourage users of gas and oil to switch (i.e., taxes on all types of combustion of fossil fuels). This may happen by 2030 or later, but eventually, heat pumps will remain in use while oil and gas heating systems will no longer be common. This is not because oil or gas will run out, but because of the energy transition. If all existing reserves were extracted and burned, it would significantly exceed the 2-degree Celsius (3.6°F) climate target. Therefore, we will not face a shortage of oil or gas simply because of depletion.

A general contractor (GC) has sent me a quote that was originally prepared for other clients. The quote comes directly from the building services company; the GC has only occasionally deducted about 5% before likely forwarding it.

The following three offers are included (prices are net unless otherwise stated; I have consolidated the many individual items):

A)
- Gas condensing boiler with domestic hot water heat pump and decentralized ventilation (not sufficient for KfW55 standard, 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 for insulation layer listed)
- Radiators, installation and accessories (€385)
- €368 (one item: 10 linear meters for "Hectu Plus pipe per 25m")
- Total including VAT approximately €15,000 for the heating trade
- Zweotherm decentralized ventilation unit (2 pieces, €460 each)
- 2x Zewotherm exhaust systems
- Electrical connection supplied by customer
- Total including VAT about €1700 for ventilation (probably only living room/kitchen and exhaust in bathroom)


B)
- Split heat pump with decentralized ventilation (meets KfW55 standard)
- Stiebel Eltron WPL 08 S Trend Set 5 (€8000)
- with integral storage tank HSBC 200 liters (53 gallons)
- Installation and core drilling etc.
- Total so far €10,600
- Electrical connection for entire heating system supplied by customer
- Underfloor heating €2450 (cheaper than A)
- Insulation layers for underfloor heating supplied by customer
- Piping €1300 (cheaper than A)
- Sanha-Therm (no separate item for insulation layer listed)
- Radiators €378
- Ventilation like A but with a second exhaust unit (€1635 net, more expensive than A)
- No information about customer-supplied items, possibly included in "entire heating system"?
- Total including VAT approximately €19,500


C)
- LWZ heat pump with central ventilation system (meets KfW55 standard)
- LWZ 504 (€12,000)
- Plus accessories and installation
- Electrical connection for entire heating system supplied by customer
- Total so far €14,300
- Underfloor heating €3100 (cheaper than A, more expensive than B)
- Insulation layers supplied by customer
- Piping €1300
- Radiators €378
- Ventilation ducts €5560
- Zewotherm
- Total including VAT approximately €29,400


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

Total costs heating only net: €6500 + €385 = €6885
Total costs air-to-water heat pump only net: €10,600
Difference A-B: about €4200


Conclusion:

According to the quote, an air-to-water heat pump costs at least €4000 more, though I have not yet understood why the underfloor heating is cheaper with an air-to-water heat pump compared to a gas boiler—possibly different heating circuits? Also, items like "insulation layers supplied by customer" as well as the electrical connection for the equipment must be considered for options B and C. For A, the gas connection to the house (around €2500?) must be factored in.

According to the GC’s offer to me, the air-to-water heat pump carries a surcharge of about €7000, which is a considerable premium. Considering the €5000 bonus from the KfW bank, the air-to-water heat pump is effectively free if you organize the building services yourself.

Options B and C are comparable in terms of content, except for the ventilation technology. The ventilation system costs about €10,000 + €1700 (the decentralized ventilation included in B) = €11,700. According to the GC’s offer to me, the ventilation system alone costs about €8000 extra compared to no ventilation installed; so the ventilation system price matches the surcharge. From this, I conclude that the combined unit LWZ carries a €3700 surcharge compared to the split system; in return, it has 35 liters (9 gallons) more water content and is presumably larger overall.

In B, I see handwritten notes under the final amount and a 5% surcharge, which is probably the GC’s margin. So the above prices initially come directly from the building services company.

I am somewhat surprised by the high costs of the gas condensing boiler and the related expenses (I am not even counting the underfloor heating here). This gas condensing boiler does not include a solar system; if it did, I would agree with Grym’s statement that an air-to-water heat pump should be roughly cost-neutral compared to a gas condensing boiler plus solar thermal.

I consider the price of the ventilation system—almost €12,000—to be too high, especially since the GC offered it to me earlier for €8000.

If anyone is interested in the document I received, just send me a private message by email.

There should still be a €1500 (approximately $1600) subsidy available from BAFA for the LWZ504.