Which heating is recommended for KfW 55?

Ah ok, great. We had drilling done on Thursday and the application was submitted then. Our plumbing contact person filled out the application with the data of the planned heating system. It is planned that way and will be listed in the contract with the general contractor like that, but we haven't "purchased" the heat pump yet; in theory, we could still change the heating system. I'm not entirely sure now whether we are eligible for the subsidy with that or not (since we have already "purchased" the heating system with the fixed price from the general contractor).

If I have understood the BAFA requirements correctly, no, because you awarded the contract for the construction of the heating system with your signature to the GÜ and the application must be submitted before awarding the contract.

In the case of individual awarding at a later date, it looks different...

I have already asked myself the originally posed question.

In an offer from a general contractor (GU), the house would receive a gas condensing boiler with decentralized ventilation (according to the GU’s personal statement, however, this only concerns the large living area on the ground floor (kitchen, dining room, living room).

To achieve KfW55 we would have the following options:
a) Ventilation system with heat recovery for all rooms - €7,900
b) Air-water heat pump manuf. Rotex - €4,800
c) Brine water heat pump with ground collectors - €12,500
d) Brine water heat pump with deep drilling - €19,300
e) Stiebel/Tecalor air-water heat pump with ventilation system and heat recovery - €12,400
f) Pellet heating manuf. Wodke vivotec - price on request
g) Hybrid heating - price on request

From this I understand that the insulation is already sufficient.
I also understand from this that the prices apply to the basement (half cellar, half living space due to the slope location, the cellar is also part of the heated envelope according to the offer).

Another GU offered me controlled residential ventilation with air-water heat pump for approx. €19,000 extra and could not explain with astonishment how the other GU can offer the same for €12,400. Both offer the Stiebel LWZ 404.

However, the final price with the second GU is better; I think the first GU has mixed the surcharge for the cellar in with the shell construction.
Extremely strange, but irrelevant to the topic.

In summary, KfW55 can be achieved with gas if controlled residential ventilation is added. With the offered decentralized ventilation, it does not seem to be achievable. This may also be because the decentralized system is not planned for all rooms.

The air-water heat pump LWZ 404 also only has a seasonal performance factor of 3.45 or something similar. So no BAFA subsidy. I could not find the seasonal performance factor of the gas boiler.

From the point of view of acquisition costs, I thus see the following calculation or options for us regarding the offered gas and decentralized ventilation:

1) Controlled residential ventilation for €7,900
- Extra costs for city gas connection (€2,500) and chimney sweep (20 x €100 = €2,000)
- If the gas boiler achieves a seasonal performance factor of 1.5, you get €4,500 back from BAFA
- Immediate bonus from KfW bank = €5,000
- Interest advantage after 25 years compared to bank interest of 1.51% approx. €5,000; at 1.71 approx. €10,000 (I have calculated and read this off in a separate repayment plan in Excel)

2) Controlled residential ventilation and air-water heat pump for €12,400
- Gas connection is not required, BAFA subsidy is also not applicable
- Same advantages with KfW as above

3) Decentralized ventilation and air-water heat pump for €4,800
- as 2)
- €3,000 cheaper than gas and cheaper in consumption, but no controlled residential ventilation

The air-water heat pump therefore seems to cost €4,500 more than the gas boiler. It would have to recoup this value through lower consumption over 20 years.
If I take the statement from co2online:
"As a rule of thumb: The seasonal performance factor must be greater than the electricity price divided by the natural gas or heating oil price, each per kilowatt-hour (kWh)."

And the multiple indications, also here in the forum, that the seasonal performance factor is never really achieved like fuel consumption in cars and according to the current electricity and gas price comparison assuming prices of 25 cents and 5 cents, the air-water heat pump would need a seasonal performance factor of at least 5 mathematically, due to the smoothing rather 6.
With the above LWZ404, I consider 3 to be more realistic.

Under these considerations and assuming that the gas boiler easily achieves a seasonal performance factor of 1.5, I am currently pro gas and contra air-water heat pump. However, pro controlled residential ventilation.

If I have any error in thinking, please feel free to correct me, enlighten me.
That this is now the offer of only one GU is clear to me; according to a brief Google search, the prices do not seem entirely unrealistic. In addition, I expect a surcharge for the basement compared to the above price for the controlled residential ventilation, but I think this has nothing further to do with the distinction between GAS and air-water heat pump.

You surely mean a gas heat pump and not a gas condensing boiler.

Anything else would be new to me.

And with a gas condensing boiler and controlled residential ventilation, you do not automatically achieve KFW 55!

If the GU has a gas condensing boiler as standard, then the air-water heat pump costs extra, and if the air-water heat pump is standard, then the gas condensing boiler costs extra. Even if it is the same GU and last year the gas condensing boiler was standard and this year the air-water heat pump...

Actually, the air-water heat pump should not cost more than gas condensing boiler+Solar, rather less. But the GU sets the prices...
(Solar was included after all, it always is - or not?)

I was at the energy consultation today and also followed up again with the general contractor.
I also went directly to a construction company.

Yes, it is a gas condensing boiler + solar, not a gas heat pump.

In summary, I made the following notes:

Notes at the construction company:
Cost for a gas heating system (underfloor heating, domestic hot water tank, burner, and solar thermal) approx. €15,000
Instead, pellet heating €16,000 (without solar)
Instead, air-to-water heat pump €22,000 (without solar, integrated domestic hot water tank)

That means the air-to-water heat pump costs approx. €7,000 more.

Notes at General Contractor A:
Gas condensing boiler including solar (included in the offer)
Air-to-water heat pump surcharge €4,900 (Rotex) or €5,900 (Stiebel Eltron)
Controlled residential ventilation surcharge: €7,900 (basement, ground floor, and top floor)
Controlled residential ventilation + air-to-water heat pump surcharge €12,400 (combination unit LWZ, ventilation in basement, ground floor, and top floor)

Notes at General Contractor B:
Gas condensing boiler including solar (included in the offer)
Controlled residential ventilation + air-to-water heat pump surcharge €19,000 (combination unit LWZ, ventilation in basement, ground floor, and top floor)
(for this, overall cheaper than A)

Notes from the Consumer Advice Center energy consultation:
Electricity in the heat pump tariff is 3x as expensive as gas (15 cents vs. 5 cents).
With an assumed annual performance factor of three, an air-to-water heat pump only needs 1/3 of the energy.
In summary, gas and air-to-water heat pump therefore have about the same consumption.
The air-to-water heat pump costs at least €5,000 extra.
The gas connection costs approx. €2,500.
KfW55 is also possible with gas condensing boiler + solar.
To what extent the annual performance factor of the air-to-water heat pump is overstated and only measured at e.g. +2°C is very difficult to assess; it can only be suspected.
It is also unclear to me how much a pre-heating register consumes poorly at subzero temperatures.

According to the advisor, air-to-water heat pumps, among others, only achieve such a good annual performance factor because the electricity can theoretically be generated from renewable energies. He believes that the government will backtrack on this in the coming years. Professional associations are already demanding or requesting modifications. I have not checked these statements.

Notes based on other forums and a simple Google search on consumption of various users:
- Heating costs air-to-water heat pump per year approx. €750 - €1,200
- Heating costs gas approx. €200-500 more per year
- Over 10 years (best-before), the maximum savings are about €2,000-5,000
- So far no real winters where the disadvantages of an air-to-water heat pump come into play, last time I believe in 2010
- With additional costs for air-to-water heat pump of at least €5,000, it only pays off over a longer period

My personal current opinion:
The air-to-water heat pump is initially not worthwhile.
However, this depends on what the gas connection ultimately costs.
In the end, it will probably go like this:
- Plan house without heating (mentally gas is initially assumed)
- Have heating load calculation carried out
- Have concrete offers for concrete heating systems and the final costs made
- Sleep on it for a night
- If then there is no clear opinion in favor of the air-to-water heat pump, it remains gas