# Geothermal direct use and ground-source heat pumps: Efficiency

How a heat pump delivers four units of heat for one

Source page: https://www.materialinsights.org/energy/e_geo_direct/efficiency/

What this tab covers How much of the energy available is actually captured or extracted, in per cent: theoretical limits, laboratory records, typical new equipment and in-service averages, each with exactly what is being measured.

Direct use delivers geothermal heat with no conversion to electricity, so the relevant measure is how fully plants are used. Ground-source heat pumps are measured by their coefficient of performance (COP): units of heat delivered per unit of electricity, typically about 4 in the field.

Chart: Efficiency ranges
 In service

#### Efficiency by measure

| Measure | Range | Type | What is measured |
|---|---|---|---|
| **Carnot limit, heat pump, 10 °C ground to 35 °C floor heating** | COP 12.3^[1](https://www.energy.gov/energysaver/geothermal-heat-pumps) | Theoretical limit | Theoretical maximum, 308 K / 25 K (calculated; shallow ground is 4.5-21 °C) |
| **Ground-source heat pumps, German field test (average)** | COP 4.3^[2](https://www.zfk.de/energie/waerme/studie-waermepumpen-heizen-altbau-effizient-gasheizungen-co2) | In service | Average annual seasonal performance factor in existing homes, Fraunhofer ISE four-year test |
| **All heat pumps in the same test (77 units)** | COP 2.6 to 5.4^[7](https://www.ise.fraunhofer.de/en/press-media/press-releases/2025/fraunhofer-ise-research-project-completed-heat-pumps-provide-climate-friendly-heating-in-existing-buildings.html) | In service | Range of annual seasonal performance factors, air-source and ground-source |
| **Air-source heat pumps, same test (comparison)** | COP 3.4^[2](https://www.zfk.de/energie/waerme/studie-waermepumpen-heizen-altbau-effizient-gasheizungen-co2) | In service | Average annual seasonal performance factor, air-to-water units |
| **All direct-use geothermal, capacity factor** | 30%^[3](https://doi.org/10.1016/j.geothermics.2020.101915) | In service | Heat delivered against installed thermal capacity, 2019 world average (Lund and Toth) |
| **Ground-source heat pumps, capacity factor** | 24.5%^[3](https://doi.org/10.1016/j.geothermics.2020.101915) | In service | Same basis, 2019 world average |

#### Where the energy is lost

| Step | Loss |
|---|---|
| **Temperature lift between ground and heating system** | field COPs are about a third of the Carnot limit (calculated)^[1](https://www.energy.gov/energysaver/geothermal-heat-pumps)^[2](https://www.zfk.de/energie/waerme/studie-waermepumpen-heizen-altbau-effizient-gasheizungen-co2) |
| **Seasonal idling of heat plant** | direct-use plants run at full output about 2,628 hours a year^[3](https://doi.org/10.1016/j.geothermics.2020.101915) |

A COP of 4.3 means 1 kWh of electricity moves 3.3 kWh of ground heat, delivering 4.3 kWh. Performance is best with low-temperature emitters such as underfloor heating and in well-insulated homes, because the smaller the temperature lift, the less work the compressor must do.

#### Sources

1. [Geothermal Heat Pumps (Energy Saver)](https://www.energy.gov/energysaver/geothermal-heat-pumps) US Department of Energy, 2024
2. [Studie: Wärmepumpen heizen auch im Altbau effizient (results of Fraunhofer ISE project WP-QS im Bestand)](https://www.zfk.de/energie/waerme/studie-waermepumpen-heizen-altbau-effizient-gasheizungen-co2) ZfK Zeitung für kommunale Wirtschaft, 2025
3. [Direct utilization of geothermal energy 2020 worldwide review (Lund and Toth, Geothermics 90, 101915)](https://doi.org/10.1016/j.geothermics.2020.101915) Elsevier, 2021
4. [Fraunhofer ISE research project completed: heat pumps provide climate-friendly heating in existing buildings](https://www.ise.fraunhofer.de/en/press-media/press-releases/2025/fraunhofer-ise-research-project-completed-heat-pumps-provide-climate-friendly-heating-in-existing-buildings.html) Fraunhofer ISE, 2025

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_geo_direct/index.md)
- [Overview](https://www.materialinsights.org/energy/e_geo_direct/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_geo_direct/correlation/index.md)
- [Techniques](https://www.materialinsights.org/energy/e_geo_direct/techniques/index.md)
- [Resources and labour](https://www.materialinsights.org/energy/e_geo_direct/resources/index.md)
- [Impact on the biosphere](https://www.materialinsights.org/energy/e_geo_direct/biosphere/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_geo_direct/links/index.md)