Control climate with underfloor heating or via the ventilation system?

300-600 euros depending on the version plus the outdoor unit (also depending on the version between 800-2500) plus cables and installation.

If you plan something like this early enough, you can also build the systems centrally or into the ceilings... otherwise, you have no choice but to use the well-known wall units.

Ceiling cassette was once a topic for us, but I prefer to air-condition the rooms individually. Besides, those units are not cheap either...

Big advantage of wall units: you can also heat cheaply during the transitional period - it's quick and costs hardly anything (high COP values).

And almost all manufacturers now have design units in their series.

So in the transition period you hardly need to heat today anyway, only when it gets really cold. And then (your) brine heat pump certainly also provides high COP values. For me, the brine temperature is at least quite high after the summer. An air-water heat pump certainly does not have worse values either. And you don’t just heat the rooms where it can be cooler anyway (bedrooms!). Otherwise, I can understand the desire for an air conditioning system, but I have refrained from it because ->I personally<- have no problems with "a few weeks a bit warmer".

You don't have to, but sometimes you just want it a bit warmer for a short time – even in the bedroom.

And since underfloor heating is too slow, something like [Klima (=Luft-luftwärmepumpe)] is simply ideal.

The thing with the Cop should not be compared to the brine heat pump, but rather say that these units can heat very effectively.

I'm speaking from experience, as in our last [KFW55] apartment we definitely had a need for heat occasionally and also installed [Klima].

But it's purely a nice-to-have. At first, I only wanted the pipes laid, but unfortunately they have to stick out of the wall, which you wouldn’t want for longer...

That is probably something like with many (comfort) extras. Once you had it, you want to have it again; if you don’t know it, you don’t miss it either. (And of course user behavior regarding temperature). Since my parental home already had underfloor heating (so I don’t know it any other way), there were never rapid temperature changes for me.