По занным 2018 года в Финляндии было установлено более 800 тысяч установок, работающих от геотермальных источников.

More than 800 000 heat pumps have now been installed in Finland, and they produce 6-7 TWh of renewable energy per year.

https://www.ehpa.org/about/news/article/heat-pump-investments-up-to-half-a-billion-a-year-in-finland/

Если более подробно, то почитай заметку финского проф. геофизики:

https://www.geothermal-energy.org/pdf/IGAstandard/WGC/2000/R0778.PDF

USE OF GEOTHERMAL ENERGY: HEAT PUMPS

The vertical ground coupled heat pumps are typically installed in boreholes 80-130 m deep. Deeper holes (150-200 m) were
preferred in the 1980's. The coefficient of performance (COP), defined as the ratio of the energy produced to the energy used
by the heat pump, has increased from the values of the early installations (COP = 2.5) to about 3.3 in the modern
applications. Energy is extracted about 40-60 W/m of borehole. An ethanol-water solution is used as the heat
exchange fluid and it is circulated in a U-shaped plastic installed in the borehole.

The horizontal ground coupled systems use pipes that are buried about 1.0-1.5 m below surface and separated
horizontally by about 1.5 m. In the typical installation for a 130-150 m2 family house the total length of the pipes is about
150 - 300 m.

How Geothermal Heat Pump Systems Work