Geothermal heat pumps (GHPs), also known as ground-source heat pumps (GSHPs), are universally recognized as the most efficient heating and cooling technology available, especially in cold climates. Unlike air-source heat pumps, which struggle to extract heat from frigid outdoor air, GHPs rely on the stable, consistent temperature of the earth below the frost line—typically between $50^\circ\text{F}$and$60^\circ\text{F}$($10^\circ\text{C}$and$15^\circ\text{C}$) year-round. This stability allows them to maintain peak performance even when outdoor temperatures plummet to sub-zero levels.

Understanding a geothermal system’s true efficiency requires focusing on two key metrics: Coefficient of Performance (COP) for heating and Energy Efficiency Ratio (EER) for cooling.

COP: The Crucial Metric for Cold Climates

The Coefficient of Performance (COP) is the most critical rating for assessing a GHP’s performance in a heating-dominated, cold climate. COP is a ratio of the thermal energy (heat) the system produces to the electrical energy it consumes.

• A standard electric resistance furnace has