Energy Saving Ordinance, KFW55, KFW40 or KFW40 Plus

It will probably never pay off to build something better than the energy saving ordinance. So it is the green idea, or other reasons. But I would not build with a homebuilder who turns a KFW 55 house into a 40, because it is pointless. If already an energy-efficient house, then with an architect who considers all points. Otherwise, you might as well save yourself the trouble.

Hello everyone, I now have to ask a few silly questions after all. We would like to have a [Kontrollierte-Wohnraumlüftung] (for comfort reasons, I am allergic, bad experiences with well-insulated houses and working full-time, etc.). We had logically set our sights on a central [Kontrollierte-Wohnraumlüftung]. Does that even make sense anymore? If you were to build according to the energy saving ordinance, it would, in my understanding, result in a suitably insulated house with a gas heating system.

Our wish would be to have underfloor heating throughout the whole house and the [Kontrollierte-Wohnraumlüftung]. How do you implement this? You often see houses that also have a solar system. Does that make sense or is it totally pointless? It probably doesn’t pay off because the electricity consumption of the [Kontrollierte-Wohnraumlüftung] is not high enough for the solar system to be worthwhile. Correct? Or is there some combination (maybe with water heating) where it makes sense?

Many thanks for the enlightening contributions. Even if this means a lot of rethinking and new reading and learning for us now.

Regards

Carina

Pretty cool how certain everyone here is that it will "never" pay off. As if everyone had swallowed a crystal ball.

You assume rising energy prices. I do too, if only because of inflation. The electricity price is formed mainly from taxes, less from changes in producer prices. With gas, it's different; this is a globally traded commodity and depends on the oil price. Very prone to fluctuations and currently at a low, so many think it's a good deal for the next 30 years. We'll see. 60€ gas can quickly become 100€ gas.

But you also note that insulation is at its limit and want to focus more on the system technology. I don't see it that way. The usual insulation material in functional walls is EPS and has at best a WLG 032, usually 035. Mineral insulations lie between 040 to 035. However, there are already vacuum insulations, the current cutting edge, which have WLG 007 to even 002. They are also available on the market but quite expensive. But: They are a good factor 5-10 thinner than comparable insulation. In the functional wall, this means that the KFW 55 standard can be achieved with a wall about 20-22cm thick compared to a 35-37cm thick wall. That is a massive gain in living space, which can be equated with money accordingly. More insulation reduces the heating load of the building, which is why heat generators can be designed smaller. Saves money in the investment, e.g. smaller heat pump, shorter geothermal drilling (if applicable). The facade also outlasts any system technology and will not be changed quickly. In 20 years your heat generator will be broken; then the insulation will again make itself noticeable in lower investment costs for the heat generator. Just a suggestion that you cannot reduce the topic to "Today I pay 60€ gas, you 50€ electricity."

Regarding funding, that is individual. We have to build KFW 55 here anyway (or at least reach that level, not necessarily go through the KFW program), in this city there is nothing else anymore in new building areas. Controlled residential ventilation is a given anyway, the leap to Kfw 40 is a small step if you simply put 2-4cm more insulation on the functional wall. So it can be worth it. For two residential units, the subsidies double, so it can be even more worthwhile. Some also find the KFW loan conditions good since they are independent of credit rating, unlike bank loans. In fact, KFW conditions have not been very interesting for us since the beginning of the year, so we will forgo KFW certification and thus the KFW loan and subsidy. But that is just a snapshot; a year ago it would have been different.

KFW 40+ costs 40T€. Hmm. There is definitely something to that if you consider the "big" jump from the Energy Saving Ordinance to KFW40. 10T€ more insulation, 10T€ ventilation system, 10T€ photovoltaics, 10T€ electricity storage. Roughly. Against that are 15T€ repayment subsidies (for which, as said, the full KFW loan must be taken), already 30T€ for two residential units... energy savings, a qualitatively better house (-> resale value), possibly income from photovoltaics or savings on household electricity, and the incalculable comfort of controlled residential ventilation.

For the Energy Saving Ordinance, controlled residential ventilation should be sufficient instead of solar. At least that’s how the standard Energy Saving Ordinance house of our general contractor looks. Although decentralized, it wouldn’t be my choice, but at least it’s something. I would skip additional solar. I’d rather lay out the underfloor heating more closely so that it also works with the lower feed temperatures of a heat pump. Why shouldn’t a central controlled residential ventilation make sense? If it is a desirable comfort element for you. It was for us as well. Due to the good KfW interest rates last year, the step to KfW 55 was worthwhile for us. At the moment, it wouldn’t be anymore. If KfW 55 is targeted, look for appraisers. Ours costs 2500€, half of which is paid by KfW.

Moreover, the statement about the KFW expert at the beginning of the thread is nonsense. On the one hand, the costs are covered half by KFW, on the other hand, even for a house under the Energy Saving Ordinance, corresponding services for the thermal insulation certificate must be provided, which are not free. To be precise, KFW experts and energy consultants who create thermal insulation certificates are usually the same person.

Facts. The current Energy Saving Ordinance requires everyone to partially use renewable energy for new buildings. The cheapest to manufacture is the gas condensing boiler combined with solar for water heating. The solar can easily be replaced by a controlled residential ventilation system with heat recovery. More is always needed, less is not. However, the valid Energy Saving Ordinance also allows district heating from renewable energy, biogas, or combined heat and power plants. Where available, surely the cheapest. In purchase.
It is also a fact that every house requires, besides plans and structural engineering, the Energy Saving Ordinance proof in the form of an energy demand calculation for the building permit, which is carried out by the appropriate engineering office. This is also handed over to the builder as proof and is part of the house documents.
It is also a fact that when we talk about indoor climate, even a normal Energy Saving Ordinance house is very airtight, so it only makes sense to provide some kind of forced ventilation. Here, the cheapest way is the exhaust fan in the bathroom, as that is where the most moisture occurs, plus window frame vents all around. The controlled residential ventilation system is a comfort variant that also consumes energy, as it is electrically operated.
Karsten