Underfloor heating: Are the pipes tight enough?

In my opinion, the house will not get properly warm. I find the composition of the building envelope not well thought out enough. Why did you have a geothermal system installed in an old building with old windows? This money would, in my opinion, have been better invested in windows and a gas boiler.

Many thanks for your numerous responses, especially BeHaElja. Based on your calculation template, I continued calculating, used better values here and there (insulation, target temperature) and worse ones elsewhere (windows), took the heat loss performance seriously, and then barely made it with the design temperature and a slightly increased flow temperature.

What’s reassuring in addition:
* The building cannot be insulated without making it uncomfortable. But we compensate for the ecologically unreasonable decision to live there by not "overheating" like maniacs; that is, 18°C is warm enough. And we and the houseplants can also survive 15°C sometimes, if it actually becomes winter outside again.
* There will eventually be a Swedish stove :-)
* Those underfloor heating zones not covered with cement tiles can also be run at higher flow temperatures.
* Last but not least… inherently obvious, but still somewhat surprising, is that a closer pipe spacing would only mean about 10% more output.

So we’ll take the risk.. :-)

Thanks again for your support. It’s great that this forum exists!

Three notes:
- What kind of ceiling do you have there - or what is above the room?
- Do not use geothermal energy... Gas is much more forgiving here - and if you really drill, better drill deeper than barely reach 15° indoor temperature.
- For living spaces: 15° is COLD!; 18° is COOL!; 20° is okay; 21° is often taken as "standard".

Between 250mm and 100mm there is a 50% as well as a 10% performance difference. For purmo, there are calculation tables.

: The ceiling is basically reed plaster - air - strip floor of the upper story. Heating is done with radiators upstairs. Geothermal energy is already installed and has served us for a whole winter, with (far too few) radiators. That was certainly somewhat suboptimal, also for the heat pump, but it was warm enough. Why should gas be more "tolerant"? I don't understand the connection. In my eyes, everything here is fine as long as it delivers a flow temperature of 35°, right? Agreed, 15° is cold, but it’s also not constantly -14° outside. And otherwise, whatever. In my office I have (voluntary) 12°, in the bedroom 5°, so 15° in the living room will feel quite good :-) I think if you practice freezing a little, 15° doesn't feel worse than 23°. So the ones suffering are mainly our guests ;-) .. and for them, the Swedish stove is supposed to take care of that..

: Thanks for the tip, found the tables and can use them very well. I only have 25cm in the middle of the room, towards the edge it’s often 10cm, even 5cm away. I’d say on average I have about 18cm. Then we would still be closer to 20% than 10%. That obviously stinks to me.. :-/

As always, many thanks for your time!

As I said - I am just a layman, but... I don't want to say anything bad about the pipe manufacturer, but he certainly benefits from selling pipes ;-) U-value says otherwise (30° supply, 45 mm cement cover, 17 mm pipe) between 25 cm and 10 cm with tiles: 22% between 25 cm and 10 cm with parquet: 20% between 18 cm and 10 cm with tiles: 12% between 25 cm and 10 cm with parquet: 8% although I can't guarantee that the U-value is correct.

Since there are similarly heated rooms above, you can initially exclude them when making rough calculations. I was more concerned about the costs - if you overstress the brine too much, it gets colder and your heating works less or is less efficient - and that excessively.