Is KfW55 worth it instead of KfW70 with an additional cost?

Hi Watcher, financially it probably won’t be worth it. You don’t say how big the house is, but with about 150 sqm you’ll end up with around 50 € per month in heating costs. The savings potential, as nordanney already writes, will be around 10 € per month. At best! That means you’ll save 120 euros per year, which you have to pay for with a 2500 euro investment. You also have to pay interest on the 2500 euros, so you’re left with about 100 euros in savings. And that means an ROI of 25 years. From a financial perspective, that’s a clear: forget it! If you want to do it for your green conscience, that’s a different story. Although there are also plenty of example calculations showing that at some point the effort for additional insulation is no longer ecologically worthwhile. In other words, eventually there comes a point where additional insulation doesn’t even save as much energy as was used for its production. Depending on the calculation, this point lies somewhere around Kfw 70 to as low as KFW 40. Which calculation is correct, nobody really knows. But what is certain is that ecologically the “jump” from KFW 70 to 55 doesn’t bring much more. If you want to do something for the environment, bike to work or even better, skip air travel. One flight to the south with the family (Düsseldorf to Crete) and you’ve roughly blown the annual consumption of your heating into the air! From a Caribbean vacation you could heat your house for several years! The only remaining argument might be a possibly better resale value of a KFW 55 house. In 20-30 years there will probably be energy regulations that will make all our houses look like “drafty shacks.” Who knows…?!? Best regards, Andreas

What is happening now with the €8000 extra cost? Insulation? Technology? Magic? You haven't answered that question yet.

@ - but I wrote that in the first post that something would have to be done about insulation and possibly windows. I am still waiting for a precise statement about what exactly. My concern was only whether one should generally consider it or just stick with KfW70. If I were to really save 5€ per month in theory, then I can save myself the additional cost of currently 2500 €, provided the extra costs really stay at 8000 €.

Amazing that the company can already state the amount of €8000, but not the exact list of measures. I thought it would be the other way around, that you first calculate the necessary measures and then try to determine the costs for them.

Then you might save 5-15 € per month - that's not much. Completely disregarded, because it is intangible, is the value of the house itself. Which house would you prefer to buy today (a 20-year-old property), the energetically very well-built house from back then or the drafty shack? That’s how people will think about YOUR house in 20 years as well.

The savings alone therefore hardly justify the investment. The difference really isn’t significant. And in 20 years, both houses will be considered "drafty shacks," as everything will have developed in such a way that a 20-year-old house will be viewed as equally good/bad, regardless of whether it meets KFW55 or KFW70 standards. So, even with regard to a possible resale value, in my opinion, the investment cannot be justified. Or did I misunderstand you? Best regards