CHOOSING THE HEAT SOURCE

In heating systems, three heat sources are most commonly used: groundwater, soil, and air. The first two require an additional investment in a heat extraction system:

Groundwater: boreholes for extracting and returning water to the aquifer
Soil: ground collector (horizontal or vertical)

An air-to-water heat pump does not require additional external installations, but choosing the right location is crucial. Its efficiency depends on the air temperature, which varies throughout the year — dropping below –20 °C in winter and exceeding 35 °C in summer.

How to choose the optimal heat source?

The basic rule for choosing a heat source is: the higher the source temperature, the higher the coefficient of performance (COP) and the lower the heating costs.

When looking for an available heat source, you should always start with the one that offers the highest average annual temperature. If this is not available, sources with lower temperatures are considered step by step, following the guidelines below.

	Ground (ground collector or geothermal probe) More >>	Water (groundwater) More >>	Air More >>
Temperature throughout the year	Fairly constant between 0°C and 9°C.	Constant between 9°C and 13°C.	Highly variable from -20°C to +40°C.
Efficiency	Typically achieved COP ranges from 4—5.	Typically achieved COP ranges from 4.5—6.	Depends on the quality of the heat pump. COP of European manufacturers ranges from 3—5 (low-cost heat pumps 1.5—3.5).
Availability	Everywhere; for geothermal probes, water protection areas or underground caves (karst) may be an obstacle. Availability and quality do not change over time.	In some places; where quality groundwater is available and it is not a water protection area. Quality and water level may change over time.	Everywhere; less common in very cold climates. Availability and quality do not change over time.
Installation	Simple; can be done independently (ground collector). Complex; requires a qualified drilling contractor (geothermal probe). Usually, the contractor completes the heat source installation, meaning they bring the connection pipes into the building and finish the groundworks. The planning and execution must be carefully prepared.	The suction and discharge well are installed by a specialized drilling contractor using appropriate equipment. Typically, the contractor provides a turnkey heat source, bringing pipes and cables from the wells into the building and completing the earthworks.	Simple; can be done independently with a proper base and connection to the boiler room. Complex; carried out by a contractor as a turnkey solution.
Installation duration	1—3 days	1—2 days	1—2 days
Required permits	Mining permit for geothermal probe (provided by the contractor).	Water permit and mining permit for wells deeper than 30m (provided or assisted by the contractor).	No special permits required. Must comply with noise regulations.
Investment cost	Medium for a ground collector, high for a geothermal probe.	Medium	Low
Subsidy	High (final investment cost is similar to that of an air-to-water heat pump)	High (final investment cost is similar to that of an air-to-water heat pump)	Low
Common mistakes and issues	Incorrectly sized geothermal probe or collector for heat source use; Lower thermal output from the ground.	Poorly constructed suction or discharge well – water contains too much sand, suction well does not drain properly; Shallow wells (1—4m) may cause very low water temperatures when snow melts; Failure to follow recommendations for installing balancing valves, water filters, pressure gauges, and the PIL module.	Incorrect placement, obstructed air intake or exhaust, improper location, causing noise for neighbors or sleeping areas. Incorrectly sized heat pump power for demand and climate conditions.
Thermal output	For 1 kW heating power, 30—35 m of ground collector or 15—18 m of geothermal probe is required.	For 1 kW heating power, a groundwater flow of 0.23 m³/h is required.	/

Special heat sources – more >>