What a geothermal heat pump does and why it works differently

A geothermal heat pump pulls heat from the ground instead of the air. The ground stays a steady temperature year-round — usually 45 to 75 degrees depending on your location — so the system doesn't have to work as hard as an air-source heat pump does when outdoor air is very cold or very hot. In winter, it extracts that ground heat and moves it indoors. In summer, it reverses and pushes indoor heat back into the ground to cool your home.

The reason this matters for performance: an air-source heat pump loses efficiency when the outdoor temperature drops below freezing. A geothermal system keeps working at full strength because the ground temperature doesn't change with the season. That's why geothermal systems typically deliver more heat per unit of electricity used than air-source models, especially in climates with harsh winters.

Key Takeaways

  • Geothermal heat pumps exchange heat with the ground through buried pipes called a loop, which stays at a stable temperature year-round.
  • The system uses a refrigerant and compressor to move heat from the ground into your home in winter and reverse the process in summer.
  • Ground loops can be installed vertically (drilled deep) or horizontally (buried in trenches), depending on your property size and soil type.
  • Geothermal systems cost more upfront than air-source heat pumps but use less electricity and often last 25 years or longer.
  • Installation requires digging or drilling, so you need adequate land and soil that can be excavated without hitting rock or utilities.

The ground loop: how heat gets from soil to your system

The ground loop is a network of plastic pipes buried in the earth. Water or a water-antifreeze mixture circulates through these pipes and absorbs heat from the surrounding soil. In winter, that warmed fluid returns to the heat pump indoors, where the system extracts the heat and distributes it through your home's ductwork or radiant heating system.

Two main loop designs exist. A vertical loop is drilled 150 to 400 feet deep — useful when you have limited yard space. A horizontal loop is buried 4 to 6 feet down in trenches that spread across your property — it requires more land but is often cheaper to install. Some systems use a pond loop if you have a large body of water on your property; the pipes sit on the pond bottom and extract heat from the water.

The loop itself doesn't produce heat. It straightforward collects the steady warmth that already exists in the ground and carries it to the heat pump, which then concentrates and moves that heat where you need it.

The compressor and refrigerant cycle inside the unit

Inside your home, the heat pump contains a compressor, an expansion device, and coils filled with refrigerant — a chemical that changes between liquid and gas as pressure and temperature change. This cycle is the same basic process an air-source heat pump uses, but the source of heat is the ground loop instead of outdoor air.

In heating mode, cold refrigerant flows through the indoor coil (called the evaporator) where it absorbs heat from the warm fluid coming from the ground loop. The refrigerant evaporates into a gas. The compressor then pressurizes that gas, which raises its temperature even higher. The hot refrigerant gas flows through another coil (the condenser) where it releases heat into your home's air or water system. As it cools, the refrigerant condenses back into a liquid, and the cycle repeats.

In cooling mode, the system reverses: the indoor coil becomes the condenser (releasing heat from your home), and the ground loop coil becomes the evaporator (absorbing that heat and dumping it into the ground). A reversing valve switches the direction of refrigerant flow.

Why ground temperature matters for efficiency

The efficiency of any heat pump depends on the temperature difference between the heat source and where the heat is being moved. A geothermal system has a smaller gap to bridge: the ground is always moderate, so the compressor doesn't have to work as hard to move heat in either direction.

An air-source heat pump in a climate where winter temperatures drop to 0°F has to pull heat from very cold air and move it indoors — a large temperature gap. A geothermal system in the same location pulls heat from 45°F ground, a much smaller gap. Smaller gaps mean the compressor uses less electricity to do the same job. This is measured as coefficient of performance (COP) or heating seasonal performance factor (HSPF). Geothermal systems typically achieve a COP of 3 to 5 in heating, meaning they deliver 3 to 5 units of heat for every 1 unit of electricity used. Air-source systems in cold climates often fall to 1.5 to 2.5.

Installation: what happens underground and what you need to know

Installation begins with a site assessment. A contractor evaluates your soil type, groundwater depth, available space, and proximity to utilities and structures. Soil composition matters because clay, sand, and rock all conduct heat differently. Groundwater also affects loop design — if water is close to the surface, a vertical loop may be better than horizontal trenches.

For a horizontal loop, a backhoe digs trenches 4 to 6 feet deep across your yard. Plastic pipe is laid in the trenches, connected in a series, and buried. The entire loop is then pressure-tested and flushed before connection to the indoor unit. For a vertical loop, a drilling rig bores holes 150 to 400 feet down, inserts U-shaped pipe, and seals the hole with grout. Vertical installation is more precise but takes longer and costs more.

Once the loop is in place, the indoor unit is installed much like a furnace or air handler — in a basement, attic, or utility closet. Ductwork connects to your existing vents, or if you're installing radiant heating, tubing is laid in floors or walls. The system is then charged with refrigerant and tested.

Cost, lifespan, and when geothermal makes financial sense

Geothermal heat pump systems cost between $15,000 and $30,000 installed, depending on loop type, property size, and local labor rates. That's roughly two to three times the cost of an air-source heat pump. However, the lower operating cost — typically 30 to 70 percent less electricity than a conventional furnace or air-source system — can offset the upfront expense over time.

The indoor unit typically lasts 25 years or longer. The ground loop often lasts 50 years or more because it's buried and protected from weather. That long lifespan means the system is spreading its cost across decades of use. In regions with high heating and cooling demand — the Northeast, Midwest, and parts of the South — the energy savings often justify the investment within 10 to 15 years.

Geothermal makes less financial sense if you have limited land, if your soil is mostly rock, if digging would damage existing structures or utilities, or if you plan to move within 5 to 7 years. It also requires adequate space: a horizontal loop typically needs 1 to 2 acres, though vertical loops work on smaller lots.

Maintenance and what can go wrong

Geothermal systems need less maintenance than furnaces because there's no combustion and no outdoor unit exposed to weather. The indoor compressor and coils should be inspected annually, and the refrigerant charge should be checked if heating or cooling output drops. The ground loop itself requires almost no maintenance — it's sealed and buried.

The most common problems are refrigerant leaks, which reduce efficiency and require a technician to locate and repair the leak, then recharge the system. Loop leaks are rare but serious — they mean the loop must be excavated and repaired or replaced, a costly job. Proper installation and regular inspection catch most problems early. If your system is losing heating or cooling capacity, have it serviced before the problem spreads.

Frequently Asked Questions

Can a geothermal heat pump work in very cold climates?

Yes. Geothermal systems work in climates where winter temperatures drop well below zero because the ground temperature stays constant. They're actually more efficient in cold climates than air-source systems because the temperature difference between ground and indoor air is smaller than the difference between freezing outdoor air and indoor air.

What if I don't have enough land for a horizontal loop?

A vertical loop requires much less surface area — often just a small patch for the drilling rig to access. Vertical loops are drilled 150 to 400 feet deep and can work on properties as small as a quarter acre. The trade-off is higher installation cost because drilling is more expensive than trenching.

How long does it take to install a geothermal system?

Horizontal loop installation typically takes 1 to 2 weeks depending on property size and soil conditions. Vertical loop installation can take 2 to 4 weeks because drilling is slower. Indoor unit installation adds another few days. Weather and soil type can extend the timeline.

Will a geothermal heat pump work if I have a well or septic system?

It depends on location. A loop must be installed away from wells and septic systems to avoid contamination and interference. Your contractor will map these during the site assessment and design the loop accordingly. In some cases, space constraints make installation impossible.

What's the difference between a geothermal heat pump and a regular heat pump?

A regular (air-source) heat pump exchanges heat with outdoor air. A geothermal heat pump exchanges heat with the ground through buried pipes. Geothermal is more efficient because ground temperature is stable, but it costs more to install because it requires digging or drilling.