Achievable minimum temperature according to KfW55 standard

An electric towel radiator is installed in the bathroom, which is supposed to achieve 24C. There is underfloor heating in the bathroom. Only with that we can no longer reach 24C.

It is a new system with several hundred apartments. I am still checking the building description. I have never had a problem with a heater. Every new building is probably an adventure.

Towel radiators are quite common, as the highest temperatures are to be reached in a small exhaust space in the bathroom. 24 degrees are quite ambitious with the flow temperatures commonly used today anyway. I would guess that the flow rate is set too low. But to be sure, the question is what exactly the tenant has set on the thermostats. Are they all already set to the highest level? Do all valves in the manifold then open?

Yes, the highest level. The valves also open. I ask the neighbors how warm it gets there.

How is the apartment situated in the building? Are there more exterior walls than with the neighbors?

The topic becomes exciting when it actually gets to -15 degrees.

In my opinion, one of the following possibilities could exist:
- the entire heating design was done incorrectly (design or technical - heating circuits, for example, turned down more or less)
- hydraulic balancing went wrong
- heat generator is so undersized that it just manages to reach 20 degrees in the apartment at "warm" autumn temperatures and in winter it might only get to 12 degrees
- heating (heating curve) is set so low that no more is achieved. This could be adjusted on the heating system.

Stupid question, but I've already read everything imaginable here in the forum...
But your tenant is keeping the windows closed, right?
I vaguely remember a post recently where the OP complained about high heating costs, but it turned out that she had the window open all the time in the pantry because of the vegetables... :D

Otherwise, I agree that KFW55 does not exclude higher temperatures. We have just built with KFW55 and are experiencing the first heating period. To heat nicely dry, we keep it cozy warm throughout the house (T-shirt temperatures). That's no problem if you want to spend the money for it.

I hope the house is not heated with a possibly undersized heat pump system? Then there would be enormous problems in a proper winter, but probably not only for your tenant. I would also be interested in what the neighbors say.