Geothermal probe: costs, installation, benefits and experiences (2025)
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Stefano Fonseca ist Ingenieur für Energie und Umwelt mit über sechs Jahren Erfahrung in der technischen Gebäudeausrüstung (TGA). Er kombiniert technisches Fachwissen mit einer Leidenschaft für verständliche Kommunikation. Seit mehr als fünf Jahren schreibt er als freiberuflicher Redakteur über erneuerbare Energien und nachhaltiges Wohnen, insbesondere über Photovoltaik und Wärmepumpen.
Deep underground, there is a heat source that is constant, invisible and surprisingly efficient. Anyone who develops them makes themselves independent of fluctuating energy prices and uses the power of nature directly from the ground. In this article, you will learn everything you need to know about the geothermal heat pump with probe — from the costs to the installation process.
What is a geothermal probe?
A geothermal probe is a system of pipes inserted vertically into the ground which supplies thermal energy to the geothermal heat pump from deeper layers of the earth via a circulating brine liquid. It is a space-saving alternative to area collectors, as it requires significantly less land space.
How does a geothermal heat pump with a probe work?
In the case of a geothermal heat pump With the probe, brine (a water-glycol mixture) flows through the geothermal probe in a closed circuit and absorbs the stored geothermal heat. This heat is directed to the heat pump, where it is converted into a refrigerant in the evaporator. The compressor increases the pressure of the evaporated refrigerant, causing its temperature to rise. In the condenser, the heat is transferred to the heating and hot water system. The cooled refrigerant is then expanded via the expansion valve and returns to the evaporator — the cycle starts again.
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How is a geothermal probe constructed?
A geothermal probe consists of one or two U-shaped plastic pipes that are inserted into a vertical borehole. A frost-protected brine liquid circulates in these pipes, which absorbs geothermal energy and transports it to the heat pump. The probe is part of a closed circuit and is inserted 40 to 100 meters deep into the ground, depending on heating requirements.
How much does a geothermal heat pump with probe cost?
A geothermal heat pump with a probe costs a total of between 27,000 and 45,000 euros. The geothermal probe alone costs around 8,000 to 12,000 euros. There are also costs for drilling, installation and connection of the heat pump to the heating system.
Which requirements must be met?
The requirements you must meet for a geothermal heat pump with a probe depend primarily on geological conditions and official requirements. In addition, the heating load of your building plays an important role. The following are the key points you need to consider:
- Sufficient drilling depth: Your property must allow drilling of 40 to 100 meters deep. This is the only way the probe can extract enough heat from the ground.
- Geological suitability: Soil conditions must have good thermal conductivity. A solid surface such as rock or clay is ideal. A probe cannot be installed in loose or water-bearing layers.
- Heat load calculation required: Before planning, you must calculate the heating load of your house. The depth and number of probes depend on this.
- Approval requirement: You need a water permit to drill. You can obtain this from the lower water authority in your federal state.
- Maintain minimum distances: The probe must maintain a certain distance from neighboring properties, buildings and other lines. This protects against subsidence or damage.
How does the installation work?
The installation of a geothermal heat pump with a probe is carried out in several steps, which must be built on top of each other and carefully planned. In doing so, both the deep drilling as well as professional connection to the heating system play a central role:
- Get approval: Before installation, you must apply for a permit from the responsible water authority. Drilling may only be carried out after approval.
- Carry out drilling: A specialist company drills one or more vertical holes up to 100 meters deep. Drilling is done with special equipment and usually takes one to two days.
- Insert geothermal probe: The U-shaped plastic probe is inserted into the borehole. The hole is then filled with thermally conductive material.
- Connection of brine pipes: The probes are connected to the heat pump in the house via insulated lines. The brine circulates in a closed circuit between the ground and the heat pump.
- Installing a heat pump: The brine-water heat pump is installed in the technical room and connected to the heating and hot water system.
- startup: After installation, a specialist company tests all functions. The system is filled, vented and adjusted to its efficiency.
How deep can a geothermal probe be drilled?
A geothermal probe is usually drilled up to 100 meters deep. For greater depths, a permit under the Federal Mining Act is currently required - which makes the entire approval process more difficult. A Draft law of September 2024 provides for this limit to be raised to 400 meters. Then only the rules of water law would apply. However, the law is not yet in force (as of June 2024).
Do geothermal probes require approval?
Geothermal probes require approval. For every deep borehole, a water permit must be applied for from the competent authority, as drilling may affect groundwater.
How many geothermal probes are necessary?
For a single-family home, a geothermal probe is usually sufficient. Depending on heating requirements, however, two probes may also be required. You need a probe length of around 10 to 15 meters per kilowatt of heating capacity.
The exact number and depth depends on the extraction capacity of the soil. Dry sand provides less heat than moist clay or rock. In highly conductive soil, 80 meters are often enough; in unfavorable soil, a probe can be drilled up to 100 meters deep or several probes are required.
How much space do I need?
For a single-family house with 150 square meters of living space and a heating capacity of 6 kW, you need approximately a probe with a depth of 80 to 100 meters. A free area of around 10 to 15 square meters on the property is sufficient for this.
You only need a small plot of land for a geothermal probe, as the drilling is vertical. A distance of at least 6 meters should be maintained between several probes. Depending on the federal state, a distance of 3 to 5 meters from the neighboring property is required.
How long does a geothermal probe last?
A geothermal probe generally lasts over 50 years. The plastic pipes are particularly robust and corrosion-resistant, so that when properly filled and installed, they can remain in the ground almost maintenance-free.
What experiences do users have with a geothermal heat pump with a probe?
Users report overwhelmingly positive about geothermal heat pumps with a probe, particularly with regard to the stable heating output and the low volume of the system. In Heat pump forum Users point out that the drilling work was quick and clean and that operating costs have fallen significantly compared to previous heating systems. In Energiesparhaus Forum However, there are also critical voices: Some users complain about high investment costs, unexpected drilling problems and poor planning by specialist companies. Experience shows that thorough planning and serious execution are decisive for successful operation.
What are the advantages and disadvantages of geothermal probes?
Geothermal probes offer high efficiency, require little space and also enable passive cooling in summer. However, they involve high initial costs and a permit requirement. They are particularly suitable for buildings with permanent heat requirements and stable surfaces.
What alternatives to geothermal probes are there?
Alternatives to a geothermal probe are Area collectors, well systems (groundwater heat pumps) and air-water heat pumps. Area collectors use near-surface geothermal energy in horizontal pipe systems, well systems extract heat from groundwater and air-water heat pumps use ambient air as an energy source. The choice depends on the size of the plot, groundwater resources, legal requirements and the budget.
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