Heating system in old buildings with geothermal heat pump, underfloor heating, etc.

Hello everyone, I have a question. Over the weekend, we looked at a single-family house that was built in 2004. It has a ground source heat pump, underfloor heating on the ground floor, and "normal" radiators on the first floor. Now we took the time to deal with the heating system a bit and came across the fact that the use of "normal" radiators is not optimal for the ground source heat pump. Does anyone have experience with this? If the configuration is very disadvantageous, the question arises whether retrofitting is possible without problems and what it would cost for about 65sqm? Best regards, Jenny

No is not optimal. The flow temperature should be as low as possible. Maybe you can find out how the radiators were sized. Maybe they are low-temperature radiators with 40°C flow temperature at design temperature, then that works.

There should be two heating circuits, one for the upper floor and one for the underfloor heating on the ground floor. If that is not the case, check the flow temperature. That is of course difficult now, better in winter at 0°C. It should then be at a maximum of 35°C throughout the entire system, then everything is fine.

In general, radiators + underfloor heating are a smaller problem with geothermal heat pumps than with air-water heat pumps.

Retrofitting underfloor heating in the upper floor means either removing the screed or laying a thin-layer system (approx. 2cm build-up, approx. 100-130 €/m²). Re-doing the screed with underfloor heating is probably similarly expensive.

It would be easier to retrofit low-temperature radiators, preferably sized as large as possible.

2004 is not really an old building. Just ask the previous owner what he pays monthly for heating costs/heat pump electricity - if it's reasonable, I wouldn't worry about it. Installing underfloor heating on the upper floor will probably never pay off.

Thank you for your answers. According to the owner, the consumption costs are 800 euros per year. But according to the owners' statement, they don't need it warm on the upper floor [OG] either. We do, though... ;)

Then calculate in the worst case with 150 to 200 euros more heating costs per year. With a minimum expense of 10,000 euros for the new screed, underfloor heating, new floor coverings, etc., you can heat significantly warmer for a very long time. Financially, it will not be worth it at all.