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

What also confuses me is that the pipes are laid almost like a "snake" or, in other words, in a serpentine pattern? As far as I know, they should always be laid in a spiral shape, starting with a wide spacing that gradually gets closer, and then spacing out again in between. In your case, you also have areas with different temperatures, so the water cools down as it flows. The spiral shape helps to balance this out to some extent.

Regarding the spacing, for a KfW70 house (built after 2009) with calcium silicate bricks plus 16cm (6 inches) of insulation, we have a pipe spacing of less than 10cm (4 inches), and I run the heating with about 30°C (86°F) supply temperature at 0°C (32°F) outside temperature. However, our living room is around 24°C (75°F), and I really don’t understand how anyone can tolerate 15°C (59°F). You could probably only sell or pass the house on to very tough individuals or experienced divers, if that ever becomes an option...

If I want to commission a high-quality heating installation that feels very comfortable with underfloor heating, do I need to specify a very low supply temperature?

How many square meters should a single heating circuit cover at most? Or, what factors determine the number of heating circuits needed?

What key points should I pay attention to in the quotes from heating installers? In other words, what are the essential aspects to consider?

Is an installation "based on calculations" sufficient?

Thank you.

PS: This concerns a gas boiler with underfloor heating, no solar system, but with controlled residential ventilation; KFW 100 house.

Amateur opinion:
You should discuss the design temperature – the lower, the better (for gas, don’t overestimate this) – the heating load must be calculated per room. Bathrooms or rooms with many windows (living areas) are often critical. In my opinion, additional costs for the pipes are rather negligible if you find a fair supplier.
It’s less about the square meter area and more about the pressures or the length of the heating circuits – I seem to remember that a certain balance should be maintained here.
If you contract individually, pay attention to who is responsible for the screed insulation. Have the details explained, such as the edge strip insulation – how is it sealed and applied?
Make sure the pipe diameter is not too small (higher pressure), but also don’t push your heating engineer into unfamiliar territory… experienced professionals usually know what they are doing.
From my own experience: don’t overcomplicate – in the end, endless optimization saves 2 euros a month. So yes, if the calculation was done well, that should be sufficient.

We were told that for a 17mm (0.67 inch) pipe, the maximum length of a heating circuit is 120 meters (394 feet). Depending on the pipe spacing, this results in about 10m² (108ft²) per circuit.