Design of underfloor heating for KFW 55 house with ventilation system

If I understand the tendencies here correctly, then (let's take the OG, for example) smaller installation distances would probably lead to two heating circuits in each bedroom, right? Otherwise, the pipes would be too long?

Right, the lengths should not be too long, you have to see what the Heizi is willing to do. Definitely under 100m. For example, we have 4 loops in the living room, placed tighter in front of the window, omitted under the kitchen cabinets/island.

Correct, the lengths shouldn't become too long, you have to see what the heating engineer is willing to do. Definitely under 100m. For example, we have 4 loops in the living room, placed tighter in front of the window, omitted under the kitchen cabinets/island.

The discussion about leaving out heating loops under kitchen cabinets is also a thing in itself. If the kitchen is on an exterior wall, hardly any general contractor will agree to it because they fear it could become too cold there and the room air could condense = risk of mold. Another aspect is that if the island is no longer going to be there in 20 years, you get a cold spot. We are also still facing this decision and will probably have the island included, but not under the kitchen unit since it is on an interior wall.

When we built in 2014, the general contractor only planned 20cm stainless steel piping for the heating with 45°C supply temperature. That was a bit too much, especially considering the gradually increasing demand and market readiness of heat pumps. So we had it designed for about 1000€ with 10cm stainless steel and approximately 35°C supply temperature. My boiler’s heating curve has been set for several years at -5°C -> 32°C supply temperature, 0°C -> 30°C supply temperature, and +7°C -> 28°C supply temperature. The place is always warm, 21+ degrees (even the wife walks around the house in short clothes in winter :p). What I want to say is, even if planned for 35°C, you can definitely go lower and it still stays warm.

Right, and that is the perfect example of why you should not be satisfied with something like an 18cm laying distance.

Hello,

just spoke with the heating engineer. Good conversation, I would say. We are going up to 22° in all living and sleeping rooms. He doesn't use the stud mat at all, but staples it, and that way we are not so rigid. He would actually be reluctant to have two heating circuits upstairs in the bedroom, because first, the heating circuit distributor would have to be enlarged, and secondly, he believes he can manage well with a maximum of 120 meters per pipe. Downstairs, he still has space for more heating circuits, at least. We have now agreed on laying distances of max. 15 cm. I could live with that. In the bathrooms, due to the covering thickness, he can still tweak something; he takes the calculation only as a guideline. We will have to pay for the pipes partly ourselves. Otherwise, he won't make it with the cost cap of the general contractor. I am now satisfied that he was so open to adjustments.

One more question: will we still get the KfW funding? There can't be any problems with a change in the laying distances, right? To my understanding, that doesn't play a role there?