A geothermal heat pump (GHP), also called a ground-source heat pump (GSHP), exchanges heat with the earth rather than outdoor air. Because ground temperatures remain relatively stable year-round (typically 45–75°F depending on location), GHPs operate at consistently high efficiencies regardless of outdoor conditions.
How Geothermal Systems Work
A loop of buried pipe circulates fluid that absorbs heat from the earth in winter (for heating) or dumps heat into the earth in summer (for cooling). This heat is then transferred to or from the building’s air distribution system via a heat exchanger and refrigeration cycle inside the unit.
Loop Configurations
- Horizontal closed loop: Trenches 4–6 feet deep, requires large land area
- Vertical closed loop: Boreholes 150–400 feet deep, suitable for small lots
- Pond/lake loop: Coils submerged in a nearby water body
- Open loop: Uses well water directly, requires adequate water supply
Efficiency Ratings
GHPs are rated by COP (heating) and EER (cooling). Typical COPs range from 3.0–5.0, meaning 3–5 units of heat energy delivered per unit of electrical energy consumed. This far exceeds the efficiency of air-source heat pumps in extreme cold.
Cost Considerations
Installation costs are high ($15,000–$30,000+) due to drilling or excavation. However, the federal tax credit (30% under IRA Section 25D) and lower operating costs typically yield payback in 5–15 years. Systems last 20–25 years for the heat pump unit and 50+ years for the ground loop.