ᐅ Heating system in an older building with a ground source heat pump, underfloor heating, and more.

Hello everyone,
I have a question. Over the weekend, we visited a single-family house that was built in 2004.

It has a ground source heat pump, underfloor heating on the ground floor, and conventional radiators on the first floor.

We took some time to look into the heating system and found that using conventional radiators is not ideal for a ground source heat pump.

Does anyone have experience with this?

If this setup is very disadvantageous, is it possible to retrofit without problems, and what would it approximately cost for about 65 sqm (700 sq ft)?

Best regards, Jenny

No, that’s not ideal. The supply temperature should be as low as possible. Maybe you can find out how the radiators were sized. Perhaps they are low-temperature radiators designed for a 40°C (104°F) supply temperature at the design temperature; if so, that would work.

There should be two heating circuits: one for the upper floor and one for the underfloor heating on the ground floor. If that’s not the case, check the supply temperature. That is of course difficult now, better to check in winter at 0°C (32°F). The temperature throughout the system should then be a maximum of 35°C (95°F) to keep everything balanced.

In general, combining radiators and underfloor heating with ground-source heat pumps is less problematic than with air-to-water heat pumps.

Retrofitting underfloor heating on the upper floor means either removing the screed or installing a thin-layer system (about 2cm (0.8 inches) build-up, around 100-130 €/m²). Renewing the screed with underfloor heating is likely similarly expensive.

It would be simpler to retrofit low-temperature radiators, ideally sized as large as possible to fit.

2004 is not really an old building. Ask the previous owner what they pay 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 responses.
According to the owner, the annual utility costs are around 800 euros. However, the owners say that they don’t need heating on the upper floor either.

We do, though... 😉

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