Lowering the supply temperature in underfloor heating more complex than expected?

as far as I'm concerned .. it's not my money. I have an annual heating demand of 8500 kWh at a NAT of -11°C. I repeat myself, I would not spend a cent just because a data sheet shows a lower flow temperature.

I also believe that it is very important that it does not happen (only) on paper. As long as a few basic rules are followed, such as no circuits that are too long or too short and not more than 10/15 cm spacing, bathroom preferably 5 cm and ideally also covering walls. Otherwise, truly catastrophic hydraulics are sometimes built.

I would invest the money in getting electricity cheaply.

The one has absolutely nothing to do with the other. You have a hydraulic system for a very, very long time, so I wouldn’t save at the wrong end!

Definitely install a wall heating system in a bathroom with 2 exterior walls. Heat output area takes precedence over laying distance. Achieving 24°C in the bathroom versus 20°C in the other rooms will be hardly possible because the rooms tend to equalize much more in a new building (the U-value of exterior components is much lower than that of the interior walls). Large deviations between the heating circuit lengths must be avoided at all costs, and the heating circuit distributors must be connected with a sufficiently large pipe (at least DN30). By the way, the larger connection pipe also results in lower pressure losses. If you can reduce the flow temperature by 5 K, that instantly means a 10% efficiency improvement for the heat pump.

Installing wall heating in the bathroom will be difficult - I fear the general contractor won’t go along with it, but I will definitely bring it up. As soon as we have the concrete planning of the underfloor heating for our house, I will definitely get back to you :)

Installing wall heating in the bathroom will be difficult – I’m afraid the general contractor won’t go for it, but I will definitely bring it up.
As soon as we have the concrete plans for the underfloor heating for our house, I will definitely get back in touch :)

If it doesn’t work, although I wonder why it shouldn’t. Simply get a stylish fan heater to turn on sometimes while bathing the kids. As an adult, 22 degrees is enough.

That's right, I have just over 22 degrees, if you have a good/even flow, that is absolutely sufficient. The temperature increases by itself through showering/drying, etc... Designing everything based on 24 degrees RT in the bathroom is very costly.

In case it doesn't work, although I wonder why it shouldn't. Just get a stylish fan heater and turn it on sometimes while bathing the kids. For an adult, 22 degrees is enough.

The fan heater (1800W) is included with us - whether it is stylish, I don't know yet ;).
An electric (towel) radiator doesn't make sense energetically, does it?