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

Hello everyone,

we are currently building a single-family house with about 230 m2 of living space, KFW 40+. A air-to-water heat pump (THZ 5.5 eco, see Tecelor page) is to be installed as the heating system.

Since 2020, BAFA has had a funding program that reimburses 35%. With the Tecalor calculator, I determined the heating load value of our house. Result: 6KW. When I now use the Tecalor calculator to check whether funding is possible, it gives the result: yes.

So far so good. However, the general contractor now says that the THZ 5.5 eco is not sufficient to receive the funding because the house is too large. That might be true, since the heating load value is higher?! Is it really the case that BAFA then sends someone to check, and if my heating load value is too high, I won’t get the funding?

I can’t really follow these statements and would appreciate it if you could enlighten me a bit.

Which annual performance factor did you calculate with which supply temperature? I suspect it depends 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.

Regardless of whether the chosen heat pump would theoretically be eligible for funding, I see the problem here of commissioning before the application is submitted.

As I read this, a contract including the mentioned heat pump and the installation has already been concluded with a general contractor. If this is correct, funding according to BAFA is unfortunately ruled out from the outset.

The problem with KfW40 is the high heating limit temperature in the annual performance factor calculator. This pushes the annual performance factor down, which is actually quite unfair. Therefore, it only works with very few air-to-water heat pump models. The heating load of the house is completely irrelevant for the annual performance factor calculation, only the design flow temperature of the underfloor heating matters. With the right floor coverings, you can also keep this nicely low at KfW40, 30 degrees works.

First, have your heating load calculated according to DIN, it will most likely be below 5kW. Or do you live in Siberian climate? What is the standard outside temperature?

For reference, I am building 205 m2 KfW55 without a basement, and the heating load is between 5.3 and 5.7 kW at -12 degrees standard outdoor temperature. The heat pump company recommended a heat pump with 5 kW heating capacity because that is more than enough. The heating load calculated according to DIN is clearly above the actual heating demand during very cold winter weeks, especially for low-energy houses.

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