ᐅ KfW 70 house, cost comparison between gas condensing boiler and air-source heat pump, cost comparison of ground-source heat pump

Hello Newsgroup,

we are also planning to build a house in Saxony and are currently still in the offer phase.
It will be an urban villa with exterior walls of about 9x9m (29.5x29.5 ft) on a slab foundation.
The likely future general contractor prefers 36.5 cm (14.4 inches) aerated concrete for the exterior walls without additional insulation.
For heating, a gas condensing boiler and additionally a solar thermal system are planned.
Triple glazing is also included as standard.

Since we are already working through the financing, the question arises whether KfW 70 makes sense.
If we get the financing through the Saxon Development Bank, we would anyway have to provide proof that we build 10% better than the Energy Saving Ordinance.

According to the seller, to achieve KfW 70, the gas condensing boiler would have to be replaced by a heat pump.

I have already read many threads on this and know that an energy calculation is needed (a little hint to €uro) to make precise statements.
Maybe some general answers can be given to my questions.

1. How much more does an air-source heat pump cost compared to a gas condensing boiler?

2. How much more does a ground-source heat pump cost compared to an air-source heat pump?

3. It is often said: If I have a better insulated house, I can save less with an air-source heat pump.
Does this mean, conversely, that the more heating energy I use, the more worthwhile an air-source or ground-source heat pump becomes?
Is there approximately a break-even point for a particular heating type?

4. According to €uro, a solar thermal system is generally uneconomical.
Is it then worthwhile to install an air-source or ground-source heat pump without a solar thermal system?
Would KfW 70 still be achievable?

Thank you very much in advance

Musketier

Musketier schrieb:
...

I have written a sufficient response, but unfortunately the forum’s system apparently did not “register” it. 😕 I don’t have time to repeat it. Feel free to ask me any questions via private message!

Best regards

Hello €uro,

thank you very much for your efforts.

Perhaps you might find some time at your convenience to provide a few brief answers.

Hello,

Musketier schrieb:
According to the seller, to reach KFW70 we would have to replace the gas condensing boiler with a heat pump.

Not necessarily; insulation can achieve that as well.

Musketier schrieb:
1. What does an air-source heat pump cost more than a gas condensing boiler?

That depends on the supplier; roughly between 5,000 and 6,000 euros.

Musketier schrieb:
2. What does a ground-source heat pump cost more than an air-source heat pump?

Again, it depends on the supplier; roughly between 12,000 and 15,000 euros. With a ground-source heat pump, the drilling is always a risk—unpredictable until the soil report is available.

Musketier schrieb:
According to €uro, solar thermal systems are generally uneconomical. Is it still worthwhile to install an air-source or ground-source heat pump without a solar thermal system? Would KFW70 still be achievable?

You can reach KFW70 without a solar thermal system.

€uro will probably provide more details on the rest.

Best regards

Hello,
just a brief comment due to some "shortcomings":

Musketier schrieb:
...According to the seller, to meet KFW70 standards we would need to replace the gas condensing boiler with a heat pump.

A general statement that requires interpretation. For KfW funding as well as the energy saving ordinance, two values must be met: Ht´ and qp´´. Question: Who is the culprit here? ;-)

Musketier schrieb:
...Maybe some general answers to my questions are still possible.

Not reliably economically, since a basic feasibility study would be necessary for that.

Musketier schrieb:
...
1. How much more does an air-source heat pump cost compared to a gas condensing boiler?
2. How much more does a ground-source heat pump cost compared to an air-source heat pump?

Considering only the initial investment is too one-sided, since later operating costs are also permanently relevant, with the specific prices of each energy carrier generally increasing progressively.
Regarding 1: Hardly any difference if you do not just look at the device! The connection costs for gas condensing boilers are often "forgotten" ;-)
Regarding 2: Here, too, the whole picture should be considered. For ground-source heat pumps, the source installation can significantly impact the investment cost.
For air-source heat pumps, the basic suitability of the building should first be checked. Generally: the better insulated the building and the milder/moderate the climate location, the more an air-source heat pump makes sense. The boundaries here are fluid ;-) So, without a solid feasibility study, it will be difficult to find the economic optimum.

Musketier schrieb:
...
3. It is often said: If I have a better insulated house, I can save less with an air-source heat pump.

What would be the reference for comparison here? ;-)

Musketier schrieb:
...Does that mean... the more heating energy I use, the more likely an air-source or ground-source heat pump is worthwhile?

Often yes, but not in every case, because the specific price of electricity is usually higher.

Musketier schrieb:
...Is it possible to estimate a break-even point for a particular heating system?

No, because every building project is unique. What makes sense for A just barely works for B and leads to a money pit for C.

Musketier schrieb:
...Is it worthwhile to install an air-source or ground-source heat pump without a solar thermal system? Would KFW70 still be achieved?

Yes! For heat pumps, consumption is always lower than demand; for gas condensing boilers, it’s the opposite. Unfortunately, the specific prices for electricity are higher than for gas, for example. Perhaps this underlines the importance of a solid feasibility study.

Best regards

Thank you both,

I will discuss the energy calculation with our general contractor and our construction supervisor.

Somehow, it feels like you’re constantly going in circles during the construction process. Understandably, the general contractor wants to provide as little unpaid work as possible before the contract is securely signed. However, before signing the contract, you need to check your financial options with the bank. If, after signing the contract, the energy calculation shows that a more expensive heating system makes more sense, you have to go back to the bank again. Ideally, with a general contractor, everything should be finalized before signing the contract.

If the general contractor refuses to carry out the calculation before the contract is signed, it might make sense to have the calculation done at your own expense initially and then offset the cost if the contract is concluded.

The same feeling of going in circles applies to the rest of the selection process.

€uro schrieb:

Musketier, post: 35346 schrieb:

3. Often it is said: If I have a better insulated house, then a heat pump saves less energy.

What would be the basis for comparison here? ;-)

I assumed that the closer I get to a passive house standard in terms of insulation, the less sense it makes to invest in a more expensive (in terms of purchase costs) but more efficient (in terms of variable costs) heating system.

Conversely, a poorly insulated house would require a costly but efficient heating system. (Assuming, of course, that the heating system can be sufficiently sized.)

A house built to energy saving regulations lies somewhere in between.

Regards

Musketier