Renovation of a semi-detached house with gas condensing boiler heating - underfloor heating? How to heat?

Hello everyone,

we are renovating a semi-detached house with a gas condensing boiler heating system.
A floor heating system is already installed on the ground floor. We also want to extend the floor heating to the upper floor.

There are 4 rooms + hallway in the basement.

Hallway: 3.7 sqm
Room 1: Technical room (distributor, server cabinet, etc.) 6.4 sqm (currently not heated at all)
Room 2: Utility room 14.9 sqm (currently not heated at all)
Room 3: 12.8 sqm (a sauna is planned to be installed here someday)
Room 4: 22.9 sqm (this will be a study and possibly later a living room (youth room))

Somehow, I find the effort to retrofit a floor heating system here a bit excessive.
On the other hand, I am told that with radiators in the basement, the whole heating system must run at an unnecessarily high flow temperature.

Is there an alternative? Or at least install a floor heating system in the large room?
In my opinion, rooms 1+2 can remain unheated, or am I mistaken?

With radiators, you really have to run a higher supply temperature. There are special low-temperature radiators, but they cost a fortune.

We have also installed underfloor heating completely in our basement. For new construction with a basement, this question basically doesn't arise. The problem with existing buildings is that the room height decreases significantly due to the floor construction. Insulation at the bottom, then the underfloor heating, then the screed with sufficient build-up. Maybe there is a lower build-up with dry screed - but I can't say anything about that.

But maybe normal radiators in the basement are the best solution for your situation. Here you can quickly raise the room temperature during sauna operation and in the study - with underfloor heating it takes forever...

Yes, that's correct, the ceiling height could become a problem.

Currently, there are tiles with a suspended ceiling.

I don't want to lose much more there. However, I don't currently know how far down the ceiling has been lowered.

Is there a very low solution for underfloor heating?

How do the costs of retrofitting underfloor heating compare to regular radiators and the high supply temperature in the long term?

Oh, the current heating system stays and is currently designed for underfloor heating + radiators. Can it even be adjusted to lower supply temperatures?