ᐅ Underfloor Heating: Are the Pipes Laid Close Enough Together?

In my opinion, the house will not warm up properly. The structure of the building envelope seems insufficiently thought out to me. Why did you install geothermal heating in an old building with old windows? In my view, that money would have been better spent on new windows and a gas boiler.

Many thanks for your numerous responses, especially BeHaElja. Using your calculation template, I did some further calculations, applying better values here and there (insulation, target temperature) and worse ones elsewhere (windows), took the heat loss rate seriously, and ended up just about meeting the design temperature with a slightly increased supply temperature.

Additionally, some reassuring points:
* The building cannot be insulated without making it uncomfortable. But we compensate for the environmentally questionable decision to live there by not overheating excessively—meaning 18°C (64°F) is warm enough. Both we and the houseplants can also manage 15°C (59°F) if winter really returns outside.
* There will eventually be a wood-burning stove :-)
* The underfloor heating zones without cement tiles can be run with higher supply temperatures.
* Last but not least—intuitive but still somewhat surprising—is that a denser pipe layout would only increase output by about 10%.

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?
- Don’t use geothermal energy... Gas is a lot more forgiving here— and if you do drill, it’s better to drill deeper rather than barely meeting the target of 15°C (59°F) indoor temperature.
- For living spaces: 15°C (59°F) is COLD!; 18°C (64°F) is CHILLY!; 20°C (68°F) is acceptable; 21°C (70°F) is often considered the "standard."

The performance difference between 250mm (10 inches) and 100mm (4 inches) is approximately 50%, while the difference between 100mm (4 inches) and 90mm (3.5 inches) is about 10%.

Purmo provides calculation tables.

@BeHaElJa: The ceiling consists of gypsum with reed matting – an air gap – and the strip flooring of the upper floor. Heating is done with radiators upstairs. Ground-source heat is already installed and has served us through one 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 considered more “tolerant”? I don’t understand the connection. In my view, anything that provides a supply temperature of 35°C (95°F) is fine, right? I agree, 15°C (59°F) is cold, but it’s not constantly -14°C (7°F) outside either. So, whatever. In my office, I keep it (voluntarily) at 12°C (54°F), and in the bedroom at 5°C (41°F), so 15°C (59°F) in the living room will feel quite comfortable :-) I think if you get used to feeling a bit chilly, 15°C (59°F) doesn’t feel worse than 23°C (73°F). The main sufferers will be our guests ;-) … and for them, the wood stove will have to do the job.

@SirSydom: Thanks for the tip, I found the tables and they are very useful. I only have 25cm (10 inches) in the center of the room, but near the edges it’s more like 10cm (4 inches), sometimes even 5cm (2 inches) gap. I’d say on average it’s about 18cm (7 inches). Then we would still be closer to 20% rather than 10%. That really bothers me.. :-/

As always, many thanks for your time!

As I said – I’m just an amateur, but...
I don’t want to criticize the pipe manufacturer, although they do benefit from selling pipes ;-)
The U-value tells a different story (30° flow temperature, 45 mm (2 inches) cement coverage, 17 mm (0.7 inches) pipe).
Between 25 cm (10 inches) and 10 cm (4 inches) under tiles: 22%
Between 25 cm (10 inches) and 10 cm (4 inches) under parquet: 20%
Between 18 cm (7 inches) and 10 cm (4 inches) under tiles: 12%
Between 25 cm (10 inches) and 10 cm (4 inches) under parquet: 8%
Although I can’t guarantee that the U-value is absolutely correct either.

Since there are similarly heated rooms above, you can exclude them for a rough calculation at first.
My main concern was the cost – if you overstrain the brine too much, it will get colder, and your heating system will deliver less power or become less efficient – and that significantly.