Renovation of heating system for existing property - condensing boiler/air-water heat pump/DHW heat pump

I will commission a heat load calculation as well as the design of underfloor heating and low-temperature radiators

Leave that and use only underfloor heating. In my opinion, the radiators have only disadvantages.

Stop it and just use underfloor heating. Radiators have disadvantages in my opinion.

Disadvantages in what sense? Because then we could only replace the radiators in four rooms and leave the floor or screed as is.

Disadvantages in what sense? Because then we could only replace the radiators in four rooms and leave the floor or screed in place.

Are in the way. Don’t fit as well into the hydraulics of the heat pump. Different heat than the underfloor heating. Higher flow temperature needed for the radiators (I’m renovating to a KfW55 house - apartment on the ground floor with underfloor heating and max. 30 degrees flow, apartment upstairs with new radiators with max. 40 degrees flow. Doesn’t matter to me as each apartment gets a heat pump.).

If there is even the slightest possibility to replace [HK] with floor, wall, sloped ceiling, or ceiling heating, I would do it. However, it will also work with low-temperature [HK]. Just not as efficiently and not as comfortably.

If there is even the slightest possibility to replace radiators with floor, wall, sloped ceiling, or ceiling heating, I would do it. But it will also work with low-temperature radiators. Just not as efficiently and not as comfortably.

We will install underfloor heating everywhere, just not in the attic. Since only the bedroom is there, the effort and cost would simply be too high for us. In our opinion, a less efficient/more uncomfortable low-temperature radiator fulfills its purpose there...

If it is not a problem, and it probably isn’t, that the bedroom is one to two degrees colder than the floor below, then that works perfectly. Then the HK can also be nicely connected to the supply line of a small heating circuit and no efficiency-draining mixing is necessary.

It’s like with so many things: once you’ve understood the rules (and the reasons behind them), you can break them now and then. ;-)

Edit: Additional idea: Install an air conditioner in the room. It helps to sleep well in the summer, also cools the floor below somewhat with open doors, and in case of emergency can also heat upstairs.