A ground source heat pump is a heating and cooling system that moves heat between your home and the earth, using the stable underground temperature as its energy source. A few feet below the surface, the ground stays between 50°F and 60°F year-round in most of the U.S., and these systems exploit that consistency to heat your home in winter and cool it in summer with far less energy than a traditional furnace or air conditioner.
How a Ground Source Heat Pump Works
The system doesn’t generate heat the way a furnace does by burning fuel. Instead, it transfers heat that already exists in the ground. A loop of pipes buried underground circulates a fluid (usually water mixed with antifreeze) that absorbs warmth from the soil. That warmed fluid travels into the heat pump unit inside your home, where it passes through a heat exchanger and transfers its energy to a refrigerant.
From there, the process follows the same refrigeration cycle found in a kitchen fridge, just running in reverse. A compressor squeezes the refrigerant into a high-pressure, high-temperature vapor. That hot vapor flows through a second heat exchanger inside your home, where a fan blows indoor air across it, warming the air and distributing it through your ductwork like a standard forced-air system. Some setups use the heat exchanger to warm water that flows through radiant floor tubing instead.
As the refrigerant releases its heat indoors, it cools and condenses back into a liquid. It then passes through an expansion valve, which drops its pressure sharply. This low-pressure liquid flows back to the outdoor heat exchanger to absorb more warmth from the ground loop fluid, and the cycle repeats. In summer, the whole process reverses: the system pulls heat from your indoor air and dumps it into the ground, cooling your home.
Why Ground Temperature Matters
The key advantage over an air source heat pump is stability. Outdoor air temperature swings wildly with the seasons, but ground temperature at depth barely changes. At the depths where loops are buried, soil typically sits between 50°F and 60°F regardless of whether it’s July or January. That means a ground source system always has a moderate-temperature reservoir to work with, rather than struggling to extract heat from frigid winter air.
This stability translates directly into performance. Research comparing the two technologies found that ground source systems maintain roughly 87% of their efficiency and 85.5% of their heating capacity as outdoor temperatures drop from 47°F all the way down to −15°F. Air source heat pumps, by contrast, retain only about 55% of their efficiency and 44.5% of their heating capacity over that same range. In cold climates, that gap often means an air source system needs backup electric resistance heating on the coldest days, while a ground source system keeps running efficiently on its own.
Closed-Loop vs. Open-Loop Systems
Most residential installations use a closed-loop design, where the same fluid circulates through the buried pipes continuously without ever being exposed to the environment. You control the water quality, contamination risk is low, and the system requires less pump energy since the fluid being pushed through one side of the loop is simultaneously being pulled back on the other side.
Open-loop systems work differently. They pump groundwater from a well, run it through the heat exchanger, and discharge it, either back into a second well or onto the surface. These systems can be more efficient because groundwater is often warmer and more thermally consistent than the fluid in a closed loop. But they depend heavily on having adequate water flow and good water quality. Mineral-rich or acidic groundwater can scale up or corrode the heat exchanger over time. Some jurisdictions also restrict or ban “pump-and-dump” designs that discharge water to the surface rather than returning it underground.
The general consensus among installers is that closed-loop systems are the safer default. Open loops can work well when conditions are right, but they carry more risk of failure and more regulatory complexity.
Ground Loop Configurations
For closed-loop systems, the buried piping comes in two main layouts.
Horizontal loops are trenched across a wide area of land, typically 6 to 10 feet deep, with trenches running hundreds of feet long. They’re cheaper to install because trenching is simpler than drilling, but they require a lot of open yard space. If your property is large and relatively flat with accessible soil, horizontal is usually the more affordable option.
Vertical loops use one or more boreholes drilled 200 to 500 feet deep, with pipe loops dropped down each hole. These are the go-to choice when yard space is limited, when you want minimal disruption to landscaping, or when rock formations close to the surface make trenching impractical. Drilling adds cost, but the system’s footprint on your property is much smaller.
Efficiency Numbers
Ground source heat pumps are measured by their Coefficient of Performance, or COP, which tells you how many units of heat the system delivers for every unit of electricity it consumes. A COP of 3.6 means you get 3.6 units of heat for every 1 unit of electrical energy you put in. For comparison, a gas furnace converts fuel to heat at roughly 0.9 to 0.98 units of heat per unit of energy, and electric resistance heating delivers exactly 1 to 1.
The most efficient closed-loop systems certified for 2025 achieve a COP of 3.6 for air delivery models. Open-loop systems perform even better, reaching a COP of 4.1, because they have access to more thermally stable groundwater. These numbers represent peak performance under test conditions. Real-world seasonal averages will be somewhat lower depending on your climate, soil type, and system sizing, but even moderate performance far outpaces conventional heating.
Installation Costs
The price tag is the biggest barrier for most homeowners. A residential ground source heat pump installation typically runs $15,000 to $40,000 or more in 2025. That range is wide because it depends heavily on which loop configuration you need. A horizontal loop on easy-to-dig soil in a mild climate lands toward the lower end. A vertical loop system drilled through rock for a larger home in a cold climate pushes toward the top.
That upfront cost is significantly higher than a conventional furnace and air conditioner combo or an air source heat pump. The tradeoff is lower operating costs over time, since the system uses a fraction of the energy. Federal tax credits and state incentive programs can also reduce the net cost substantially, though availability varies by location and year.
How Long They Last
The indoor heat pump unit, which contains the compressor, heat exchangers, and controls, has an average lifespan of 20 to 25 years. That’s comparable to a high-quality furnace. The underground loop piping, however, lasts far longer: 50 years or more, since there are no moving parts underground and the high-density polyethylene pipe used in modern installations is extremely durable. When the indoor unit eventually needs replacing, the expensive ground loop is already in place, making the second system significantly cheaper to install.
Environmental Impact
Because ground source heat pumps run on electricity rather than burning fossil fuel on-site, their carbon footprint depends partly on how your local grid generates power. But even on today’s grid, an RMI analysis found that replacing a gas furnace with a heat pump reduces climate pollution by up to 93% across all 48 continental U.S. states. That reduction begins in the very first year of installation and compounds over the system’s 15-plus-year lifespan. As the electrical grid continues adding renewable energy sources, the emissions advantage only grows.
Ground source systems also have no outdoor fan unit like air source heat pumps, so they produce no exterior noise. And because the refrigerant loop is entirely contained indoors, there’s less exposure to weather-related wear and a lower risk of refrigerant leaks over time.