Upgrade simple oil heating for hot water, underfloor heating, solar thermal

Hello everyone,

I have a house from the 1960s with an oil heating system that was installed in 2010. It is a DeDietrich GT 123. So far, hot water has been produced electrically.

As part of the renovation, several things are to be redone. Our wishes are
- continuous hot water
- new underfloor heating
- solar thermal energy

How is it generally: Is it possible to upgrade a heating system, for example with a suitable water tank and circuits, to realize the above list? Or do I necessarily need a new burner and boiler? As long as the old system is still running, I want to keep the investment costs as low as possible at this point in time.

Normally, the boiler should be able to be easily supplemented with a hot water storage tank, but it is best to inquire directly with the manufacturer. However, it is questionable whether it makes sense to give such an old system a brand-new storage tank, which may then have to be disposed of together. Although this is not your question, I have a counter-question: Why do you voluntarily want to put solar thermal on the roof? It should have become known by now that it is not worth it.

We are a family of five and as for me, I like to shower long and very hot. I think that due to the increased hot water demand, it does not look so bad economically. Or am I still wrong there?
Regarding your other objection: If I have to replace the oil heating system in, for example, 10 years, the water tank should still be able to stay in.

Calculate it for yourself. How high are your energy costs per year and how much of that is for hot water. And then ask yourself how much of that again falls on the warm season (in winter the sun doesn't shine much). Usually, in the best case, something around ~150-200€ comes out of it. Divide your acquisition costs by this value and you'll know how long the system must last without repair/total failure until you have even earned a cent with it and how much longer it would then have to last so that you can say "Yeah, that really paid off, we could take one vacation from it" ;-)

Especially with a "tight" budget, I would think about it. Do you really want to cut back today in order to (maybe) save 15€ a month in 15 years? Then rather google "Duschrohr".

Regarding the tank: I'm not a professional, but depending on the setup there are different requirements for the tank (stratified storage tank, storage tank with 1 or 2 heat exchangers, combined storage tank, design and space requirements etc.). You can probably reuse it somehow, but whether that makes sense is another matter.

Solar thermal systems also make the heating more complex, more vulnerable, and more expensive when replacing the system or exchanging parts, or unnecessarily restrictive. It is doubly not worth it.