Is a gas condensing boiler without solar thermal sufficient for KfW-70?

Hello,

...So we are also currently working on a Kfw 70 house. We have no solar, no photovoltaics. But an air-water heat pump ...

Hopefully a mild climate location. Pay attention to precise planning/dimensioning => manufacturer/device selection!

...And you have to be careful that the insulation thickness matches the windows, so that they do not sweat.

Basically, it is advantageous that AW and AF do not differ too much in terms of U-value, so that the surface temperatures do not differ too much (cold air feeling, especially with very large window areas). On the other hand, the windows are usually the "weak point" with regard to condensation. That is not so bad! An unfavorable combination is poorly or non-insulated exterior walls with very well insulated windows. Best regards.

James, you already know that the KFW Bank is now paying "an extra eye" on what is eligible for funding and what is not? We are currently also in discussions with a general contractor. Originally, we only wanted to build according to the Energy Saving Ordinance requirements, and meanwhile, we have reached Efficiency 70. Our "specialist advisor" from the general contractor says that Efficiency 70 is only a makeshift solution. I unfortunately had to show him the yellow card because of that. :p According to him, you should either build according to the Energy Saving Ordinance or directly according to EFF 55, which is the standard. :rolleyes: It should be clear to you that you have to invest for every improvement in efficiency standard. And due to rising construction costs, you should have a specialist calculate for you from when which measure to improve energy savings will pay off positively over the years.

...And due to rising construction costs, you should have a professional calculate when which measure to improve energy savings will pay off positively for you over the years.

Correct. Unfortunately, most people think they can do it themselves. A little browsing on the internet, and the problem is solved.:confused: Actually, a very demanding topic overall, in which even many professionals fail. Moreover, the hunt for so-called "subsidy gifts" leads to many bad investments. The latter even more so, the less attention is paid to proper planning/dimensioning and the more one trusts flowery sales talk.

Best regards

Hello. I am only now getting around to resolving everything. Phone call with the architect, and it turned out: Even without solar thermal and only with (geothermal) heat pump, KfW 70 is no problem. The annual primary energy demand would even allow KFW 55, only the transmission heat loss is too high for that. And we can't easily reduce that enough to make it work. Insulation under the floor slab and Y-TONG instead of Poroton is not enough yet. In this respect, the investment would probably be >4,000 euros. From builders who have so far built with our general contractor, as well as from owners of the heat pump, I hear only good things and so I see us on a good path.