ᐅ Upgrading a Basic Oil Heating System for Domestic Hot Water, Underfloor Heating, and Solar Thermal Integration

Hello everyone,

I have a house built in 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 planned. Our goals are
- continuous hot water supply
- new underfloor heating
- solar thermal system

In general, how does it work: Is it possible to upgrade a heating system, for example with a suitable water tank and circulation loops, to achieve the above? Or do I necessarily need a new burner and boiler? As long as the old system is still working, I want to keep the investment costs as low as possible at this point.

Normally, the boiler should be easily complemented by a hot water storage tank, but it is best to check directly with the manufacturer. However, it is questionable whether it makes sense to add a brand-new storage tank to such an old system, which might then need to be disposed of together if replaced.

This is not your question, but I have a follow-up: Why do you want to voluntarily install solar thermal panels on your roof? It should be quite well known by now that it is not cost-effective.

We are a family of five, and personally, I like to take long, very hot showers. I think that with the increased hot water demand, it doesn't look too bad economically. Or am I still mistaken?

Regarding your other point: If I have to replace the oil heating system in, say, 10 years, the water tank should still be able to remain in place.

Calculate it for yourself. How much are your annual energy costs, and how much of that is for hot water? Then consider how much of that is used during the warmer months (since the sun doesn’t shine much in winter). Usually, you might end up with a savings of roughly €150-200 (~$160-215) at best. Divide your initial investment by that amount, and you’ll know how long the system needs to last without repairs or total failure before you even break even, and how much longer it has to last to say, “Yes, that was really worth it—we could take a vacation from the savings.” ;-)

Especially with a tight budget, I would really think this through. Do you really want to cut back now just to possibly save about €15 (~$16) a month in 15 years? It might be better to look up “shower pipe” instead.

As for the tank: I’m not a professional, but depending on the setup, there are different requirements for the tank (stratified storage tank, storage with one or two heat exchangers, combined storage tanks, design and space requirements, etc.). You’ll probably be able to reuse it somehow, but whether that makes sense is another question.

Solar thermal systems also make the heating setup more complex, prone to faults, and more expensive when replacing the system or swapping components, which unnecessarily limits options. It is not worthwhile in either case.