New building KfW55 with gas, solar, and controlled residential ventilation with heat recovery

Hello!

We are just starting the planning of our new build and the big question currently being discussed up and down is the heating concept. We are building a detached single-family house with 145 sqm plus a converted attic (about 40 sqm) with underfloor heating (also in the attic). We want to achieve Kfw55. Building solidly with facing brick. What we definitely want as well is controlled residential ventilation with heat recovery. The most cost-effective option is the combination of gas, solar thermal energy, and ventilation. In addition, the construction companies we are currently getting offers from are offering us a KfW55 package with better insulation because otherwise it will be difficult to meet the required values. An alternative (second cheapest option) would be an air-to-air heat pump instead of gas. What are the advantages and disadvantages of these two heating systems? What are the expected monthly costs approximately? Some heating engineers told us that with gas you cannot achieve KfW55 at all? We are quite confused and everyone says something different. What are your experiences?

Thank you very much!

Is KfW55 mandatory because of funding, etc.?

We had the option gas + ST or heat pump.

Insulation for both is analogous and controlled residential ventilation with heat recovery is mandatory for both.

KFW 55 with gas, solar support, and controlled residential ventilation with heat recovery is possible and even mentioned in the reference procedure for KfW determination. Your heating installers therefore do not even know the short information sheets of the KFW. Especially since the energy consultant prepares the calculation and the heating installer only has to deliver and install. Air-to-air heat pumps do not have a good reputation here, and that seems understandable to me as well. Just look in the search function.

Are you sure that an air-to-air heat pump is meant? The direct alternative to gas is usually an air-to-water heat pump.

Thank you for your answers!

I meant air-to-water heat pump—sorry! With all the abbreviations, I don’t always keep up yet

According to the KfW information sheet, I also understood it to be a common way to achieve the 55 standard.
But then we got totally unsettled because everyone told us so far that it would rather be difficult with gas.

Now we’re definitely not going to get worked up anymore and will wait calmly to see what the energy consultant thinks.

Thanks again!

Best regards,

Xenia