KfW70 house, cost comparison of gas condensing boiler and air 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 a city villa with approx. 9x9m external walls on a slab foundation.
The probable future general contractor prefers 36.5 cm aerated concrete without additional insulation as the exterior wall.
A gas condensing boiler and additionally a solar thermal system are planned for heating.
Triple glazing is also included as standard.

Since we are already running through the financing, the question arises whether Kfw 70 makes sense.
If we were to get the financing through the Sächsische Aufbaubank, we would have to provide proof that we will build 10% better than the Energy Saving Ordinance anyway.

According to the seller, to reach Kfw70 we would have to replace the gas condensing boiler with 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 accurate statements.
Maybe a few general statements can still be made about my questions.

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

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

3. It is often said: If I have a better-insulated house, I can save less with an air heat pump.
Does that mean conversely the more heating energy I consume, the more likely it is that an air heat pump or ground-source heat pump pays off?
Can a break-even point roughly be determined for a certain type of heating system?

4. According to €uro, a solar thermal system is generally uneconomical.
Is it then worthwhile to install an air heat pump or ground-source heat pump without a solar thermal system?
Would KFW70 still be achieved?

Many thanks in advance

Musketier

...

I have formulated a sufficient response, unfortunately the technology of this forum apparently did not "accept" it. :confused: I unfortunately have no time for repetitions. Questions are welcome via PM!

best regards

Hello €uro,

thank you very much for your efforts.

maybe you will find some time on occasion to provide a few brief answers.

Hello,

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

Not necessarily; it can also be done through insulation.

1. How much more does an air heat pump cost than a gas condensing boiler.

That depends on the provider; roughly between TEUR 5 + 6

. How much more does a brine heat pump cost than an air heat pump

Again, it depends on the provider; roughly between TEUR 12 + 15. With a geothermal heat pump, the drilling is always the risk - incalculable until the soil survey is available.

. According to €uro, a solar thermal system is generally uneconomical.
Is it then worthwhile to install an air heat pump or brine heat pump without a solar thermal system?
Would KFW70 still be reached?

You can reach Kfw 70 even without a solar thermal system.

€uro will surely write something more about the rest.

Kind regards

Hello,
due to some "shortcomings" just briefly:

...According to the seller, to achieve KFW70 we would have to replace the gas condensing boiler with a heat pump.

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

...Maybe a few general statements can still be made regarding my questions.

Not economically reliable, because a basic investigation would be required for this.

...
1. How much more does an air heat pump cost than a gas condensing boiler?
2. How much more does a ground source heat pump cost than an air heat pump?

Considering only the investment is too one-sided, as the later consumption costs remain relevant in the long term, with the specific prices of each energy source progressively increasing here.
Regarding 1.: Hardly anything, if you don’t only look at the device! For gas condensing boilers, connection costs are often "forgotten" ;-)
Regarding 2.: Here too, the entire complex should be considered. For ground source heat pumps, the source development significantly burdens the investment partly.
For air heat pumps, the basic suitability must be checked first. Tendency: The better a building is insulated, the more moderate/mild the climate location, the more worthwhile an air heat pump is. The limits are fluid here anyway ;-) So, without a solid basic investigation, you will hardly find the economic optimum.

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

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

...Does that mean .... the more heating energy I consume, the more worthwhile an air heat pump or ground source heat pump is?

Often, but not in every case, since the specific price of the energy carrier electricity is generally higher.

...Can you roughly determine a break-even point for a certain heating type?

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

...Is it worthwhile to install an air heat pump or ground source heat pump without a solar thermal system?
Would you still achieve KFW70?

Yes! With heat pumps, consumption is always lower than demand; with gas condensing boilers, it is the opposite. Unfortunately, the specific prices for electricity are higher than, for example, for gas. Maybe this somewhat clarifies the importance of a solid basic investigation ;-)

best regards

Thank you both,

I will talk to our general contractor and our construction supervisor about the energy calculation.

Somehow, I feel like you keep going around in circles during construction. Understandably, the general contractor wants to provide as little unpaid work as possible before a contract is securely signed. But before signing the contract, you have to check the financial possibilities with the bank. Now, if after signing the contract it turns out from the energy calculation that a more expensive heating system makes more sense, you have to run back to the bank. And ideally, you should have everything settled with a general contractor before signing the contract.

If the general contractor refuses to carry out the calculation before the contract is concluded, it makes sense to have the calculation done at your own expense first and then settle it if the contract is concluded, right?

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

[quote="Musketier, post: 35346"]
3. Often it is said: If I have a better insulated house, I can save less with an air heat pump

What would be the basis for comparison here? ;-)
[/QUOTE]

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

Conversely, an uninsulated house would need an expensive but efficient heating system. (Provided, of course, that the heating system can be sufficiently dimensioned.)

An energy saving ordinance house is somewhere in between.

Best regards

Musketier