Heat pump and BAFA - What is true and what is not?

Which annual performance factor did you calculate with which supply temperature? I suspect it will depend on the supply temperature and your general contractor thinks that due to the size he has to increase the supply temperature and thus the calculated annual performance factor drops below 4.5.

I used the annual performance factor calculator on Tecpalor. The maximum supply temperature is set to 35 degrees by default in the calculator. The calculator then outputs an annual performance factor of 4.57 for the Tecpalor 5.5 Eco. I did not change any other values.

Have your heating load calculated according to DIN first, it will very likely be below 5 kW. Or do you live in Siberian climate? What is the standard outdoor temperature?

In my calculator the standard outdoor temperature is -14 degrees. No, I don't live there... southern Germany.

Especially with KfW40 you will hardly find a BAFA-eligible air-to-water heat pump that is small enough for your actual heating load. So you will have to oversize somewhat.

The Tecalor has the following values:

Heating capacity at A-7/W35 (EN 14511) 5.5 kW
Heating capacity at A2/W35 (EN 14511) 5.16 kW
Heating capacity at A7/W35 (EN 14511) 4.4 kW

Do these values have to match the heating load?

What do you mean by oversizing? An air-to-water heat pump with higher heating capacity values?

Use the annual performance factor calculator on Wärmepumpe Punkt de

Heating limit temperature -> Low-energy house 10 degrees

Determine the standard outside temperature for your postal code.

Select your heat pump

Do not change anything else.

If it still does not fit, you need to check the underfloor heating to see if you can achieve over 4.5 with a lower flow temperature. However, there is a risk that the BAFA may require proof.

The Tecalor will be more than sufficient in terms of heating output with the values you specify. You are almost building a passive house. Don't forget the BAFA subsidy for the controlled residential ventilation.

I calculate exactly 4.50 in the annual performance factor calculator for you. You can try it like that, but I would tend to design the underfloor heating for, e.g., 30 degrees to have a marginal buffer.

Use the annual performance factor calculator on waermepumpe.de

Heating limit temperature -> low-energy house 10 degrees

Determine the standard outdoor temperature for your postal code.

Select your heat pump

Do not change anything else.

If it then doesn't fit, you have to look at the underfloor heating to see if you can reach over 4.5 with a lower flow temperature. However, there is a risk that BAFA could request proof.

Here I get a value of 4.61. If I change the flow temperature to 30 degrees, then it is 4.78.

Doesn't BAFA always request proof? The general contractor said that after one year you have to order a craftsman who checks and confirms this?!

One more question? How is the living area still related to the topic? The general contractor said that because our house is so big (232 m2), this is a problem. How does a smaller living area affect it? The living area is not taken into account in the calculators?!

Oh, and I forgot the most important thing: Thank you very much for the support. That's really kind!!!

One more question? How is the living area now related to the topic? The general contractor said that because our house is so large (232 m2), that is a problem. How does a smaller living area affect things?

The only influencing factor: The larger the house, the greater the heating load. However, the required heating capacity per square meter of underfloor heating decreases because the ratio of the house’s exterior surface to the heated floor area becomes more favorable. This is good for the efficient operation of a heat pump if the underfloor heating is calculated accordingly.

Your construction company does not seem to have much knowledge of low-energy houses, otherwise it would not fear that the heat pump’s capacity might be too small. Therefore, it is even more your responsibility now to read up yourself, understand the matters, and question them.

The only influencing factor: The larger the house, the greater the heating load. However, the required heating output per square meter of underfloor heating decreases because the ratio of the house's exterior surface to the heating surface becomes more favorable. Good for the efficient operation of a heat pump if the underfloor heating is properly calculated.

Your construction company does not seem to have much knowledge about low-energy houses, otherwise they would not fear that the heat pump’s performance might be too small. Therefore, it is all the more your responsibility now to read up on it yourself and understand and question things.

Okay, 80% understood... Maybe I conveyed it wrongly. The general contractor’s statement was that the heat pump will be sufficient for our house regarding heating. However, he also said that we will have to install a larger heat pump in order to receive the subsidy. Therefore, we have to install the larger heat pump so that we are assured of receiving the BAFA funding. With the smaller heat pump, some value and the subsidized value will drop, and we would not get the subsidy.