Old building renovation - gas heating + radiators or underfloor heating?

How much consumption was there in past years?

"Weit runter kann".. Okay... So oil condensing boilers adjust their output. I call that modulating. That means if the system is properly set up overall and the heating system is properly chosen, the heating runs on a low flame instead of constantly turning on and off. This is more efficient and gentler on the material. This is a strong simplification, but it might help with understanding.

If there is no insulation of the top floor ceiling and possibly the sloping walls yet, that is the measure that makes absolutely the most sense. And can be done cheaply by yourself. Definitely do it before winter! With high-quality wooden windows, it is possible, if in good condition, to equip them with new glass. This is inexpensive and can potentially bring a lot.

Windows have been partially replaced (plastic).
However, I am considering replacing all the windows. (Wooden windows with double glazing).
I am currently in the process of checking what advantages wooden windows have compared to plastic windows and then I will decide.

That doesn't say anything yet; whether plastic or how glazed. The important thing is the insulation values of the glass and frame.

Except for the nice appearance, wooden windows are inferior to those made of plastic (sound insulation can be slightly better with wood due to the material; but you can also pay attention to the quality there).

Plastic windows do not need to be painted regularly.

If you want wood on the inside, wood-aluminum windows are an option; but that is among the most expensive available. But also almost the best. Even better is plastic-aluminum.

Thank you all for the explanations!

In mid-September, I will have the attic cleared out, cleaned, and then I will lay the floor with insulation material. I still have to see which material I will use for the insulation.

At that time, I will also remove the current floor. Depending on how it looks under the current covering, I will decide whether to redo everything with underfloor heating or leave it as is with radiators.

Does anyone perhaps have experience with the following heating system and can report?:

Vaillant VSC 206/4-5 90

Thanks again for the information.
Regards
Farilo

Heating brand. Whether Junkers, Vaillant, Brötje, Viessmann, Buderus, the technology is proven. Brötje and all the others all work. The radiator also has the advantage that it limits you less when it comes to floor coverings. For example, underfloor heating does not like loose laminate or wooden planks. Cork is also not great. In principle, underfloor heating forces you to something firmly glued down like vinyl or tiles. Karsten

Don’t do it.. Even glued floorboards or parquet are okay.. The 2% less efficiency is justifiable..