Berlin – September 15, 2026 -- Homeowners weighing a heating system upgrade are being pointed underground, as geothermal heat pumps promise lower long-term costs despite steeper installation prices. A new short study by consulting firm Prognos, commissioned by the Bundesverband Geothermie, the Erdwärmegemeinschaft Bayern, and the Bundesverband Wärmepumpe (BWP), finds that ground-source systems can undercut air-source heat pumps by roughly 8 percent in total annual costs over a 20-year period.
Ground temperatures stay near 10 degrees Celsius year-round
In Central Europe, subsurface temperatures remain relatively constant at around 10 degrees Celsius throughout the year. This narrow gap between the heat source and the heating system keeps operating conditions favorable even in winter, translating into consistently lower running costs.
The same system heats in winter and cools in summer
Ground-coupled heat pumps can also provide passive cooling during warmer months by tapping the earth's comparatively low temperature to regulate indoor climate without additional cooling hardware.
No outdoor unit means a quieter, less visible installation
Unlike air-to-water heat pumps, geothermal systems require no visible outdoor unit on the house or in the yard, since the heat source sits entirely underground and the pump itself runs nearly silently. Depending on the plot, installers use either horizontal ground collectors laid at shallow depth across a larger area, or vertical borehole probes drilled deeper into the ground with a much smaller surface footprint.
Boreholes can last three times longer than the heat pump itself
While Prognos notes that heat pumps are typically replaced after about 20 years, the underground borehole infrastructure can remain functional for decades longer -- the study estimates a minimum lifespan of 60 years. That extended service life is central to the long-term savings calculation.
"The study shows that heat pumps overall are cheaper than fossil-fuel heating systems. Ground-source heat pumps are even around 8 percent cheaper than air-to-water heat pumps over a 20-year period when annual total costs are considered,