The basic idea: stealing warmth from the earth

A ground source heat pump works by extracting heat that already exists in the ground and moving it into your home. Even when the air outside is freezing, the earth below the frost line stays relatively warm—usually between 45 and 60 degrees Fahrenheit depending on your location. A ground source system uses a loop of pipe buried underground to collect that heat, then uses a compressor (the same basic mechanism as a refrigerator running backwards) to concentrate it and push it into your house.

The system is more efficient than an air source heat pump because ground temperature is stable year-round. Air temperature swings wildly with the seasons, so an air source pump has to work harder in winter when you need it most. Ground temperature barely changes, so your system runs at peak efficiency whether it is January or July.

Key Takeaways

  • Ground source heat pumps bury a loop of pipe 4 to 6 feet deep (or deeper in a borehole) where earth temperature stays constant around 45 to 60 degrees year-round.
  • Refrigerant or water circulating through the buried loop absorbs heat from the ground, then a compressor concentrates that heat and delivers it to your home's heating system.
  • The same loop can run in reverse during summer to pull heat out of your house and dump it back into the ground, providing cooling.
  • Installation requires excavation and costs significantly more upfront than an air source pump, but lower operating costs recover the difference over 15 to 25 years.
  • Ground source systems work in any climate where you can dig below the frost line, but soil type and available space determine whether a horizontal or vertical loop is practical.

The loop: where heat collection happens

The heart of the system is the ground loop—a circuit of plastic pipe buried in the earth. The loop is filled with either a water-and-antifreeze mixture or refrigerant, depending on the system design. As this fluid circulates through the pipe, it absorbs heat from the surrounding soil and rock.

Most residential systems use one of two loop configurations. A horizontal loop is laid out in trenches 4 to 6 feet deep, usually in a coil or back-and-forth pattern across your yard. This requires more land but less drilling. A vertical loop (or borehole system) drills down 100 to 400 feet and loops the pipe down and back up in a single hole. Vertical loops take up almost no yard space but cost more to install because drilling is expensive.

The loop itself is passive—it does not pump or compress anything. It straightforward allows the fluid inside to absorb heat from the warmer ground and carry that heat back to the house. The actual work of concentrating and moving that heat happens in the indoor unit.

The compressor: concentrating heat to make it useful

The fluid returning from the ground loop is warm but not warm enough to heat your house directly. The compressor takes that warm fluid, pressurizes it, and forces it through a heat exchanger. This process is similar to how a refrigerator works, except the goal is to move heat into your home instead of out of it.

As the pressurized fluid passes through the heat exchanger, it releases its heat into your home's heating system—either a forced-air furnace, radiant floor loops, or a hot-water baseboard system. The fluid cools down in the process and cycles back out to the ground loop to pick up more heat. This cycle repeats continuously as long as your thermostat calls for heat.

The compressor is powered by electricity, so a ground source system is not "free" heat—it still uses power. But because the ground is already warm, the compressor does far less work than an air source pump would have to do to extract heat from cold winter air. Most ground source systems deliver 3 to 5 units of heat for every unit of electricity consumed, compared to 2 to 3 units for air source systems in cold climates.

Summer cooling: running the cycle in reverse

In warm months, the system reverses. Instead of pulling heat from the ground and pushing it into your house, it pulls heat out of your house and dumps it into the ground. The compressor runs in the opposite direction, and the ground loop now acts as a heat sink. Because the ground stays cool even in summer, the system can shed heat very efficiently.

This reverse cycle is one reason ground source systems are attractive in climates with both heating and cooling needs. You get both functions from a single installation, and the cooling efficiency is excellent because you are moving heat into a cool medium rather than trying to push it into hot summer air.

Why installation is complicated and expensive

The upfront cost of a ground source system is typically 40 to 60 percent higher than an air source heat pump, mainly because of loop installation. Horizontal loops require excavating trenches across your property—usually 300 to 600 linear feet of trench for a typical home. Vertical loops require drilling, which demands specialized equipment and a trained operator.

Your soil type matters. Clay and wet soil conduct heat better than sandy soil, so a system in clay may need less loop length. Rocky ground makes drilling expensive or impossible. The installer will assess your site and recommend whether horizontal or vertical makes sense for your property and budget.

Once installed, the loop itself lasts 25 to 50 years with almost no maintenance. The compressor and controls inside your house have the same lifespan as any heat pump—typically 15 to 25 years. Over that lifetime, the lower operating costs usually offset the higher installation cost, especially in climates where heating and cooling are both heavy users of energy.

Where ground source systems work and where they do not

Ground source systems can be installed anywhere the ground does not stay frozen year-round—which means almost anywhere in the continental United States. The system works in Minnesota winters and Arizona summers alike. The real limiting factors are space and soil.

You need either enough yard for a horizontal loop or access to drilling for a vertical loop. If your lot is small or heavily landscaped, a vertical system may be your only option. If your soil is bedrock or extremely sandy, installation costs may be prohibitive. Some municipalities also restrict ground loops—check local codes before committing.

If ground source is not practical for your home, an air source heat pump is the next best option. It costs less to install and still outperforms a traditional furnace in most climates, though it will not match ground source efficiency in very cold winters.

Maintenance and how long the system lasts

The buried loop requires almost no maintenance. It is sealed and pressurized, so leaks are rare. The compressor and indoor components need the same basic care as any heat pump: an annual inspection, filter changes, and occasional refrigerant top-ups if the system develops a slow leak.

Most ground source systems run reliably for 15 to 25 years before the compressor needs replacement. The loop itself often outlasts the compressor by decades. If you replace the compressor, you keep the loop and straightforward connect the new unit to it—you do not have to excavate or drill again.

Frequently Asked Questions

Can I install a ground source heat pump if I have a small yard?

Yes, if you can drill vertically. A borehole loop takes up almost no surface space but costs more to install. If drilling is not possible due to bedrock or local restrictions, a ground source system may not be practical for your property.

What happens if the ground loop develops a leak?

Leaks are uncommon because the loop is sealed and buried. If one does occur, the system will lose pressure and stop heating efficiently. The installer can locate the leak using pressure tests and either repair the damaged section or replace the entire loop. This is expensive, which is why quality installation and annual inspections matter.

Does a ground source heat pump work in very cold climates?

Yes, it works better than an air source pump in cold climates because ground temperature stays constant. However, in extremely cold regions, the ground can eventually cool down if the system is extracting heat faster than it is being replenished. A backup heating source (electric resistance or a gas furnace) is sometimes needed on the coldest days.

How much yard space does a horizontal loop need?

A typical home needs 300 to 600 linear feet of trench, usually laid out in a coil pattern. This typically requires a yard of at least one-quarter acre, though the exact amount depends on soil type and how many loops the installer uses. Your installer can calculate the exact requirement after assessing your soil.

Can I use a ground source system for cooling only?

Technically yes, but it is not practical. The system is designed to move heat in both directions, and running it only for cooling wastes the efficiency advantage. If you need only cooling, an air source heat pump or traditional air conditioning is more cost-effective.