Have you heard of geothermal heating but don’t understand how it works? Unlike a furnace that creates heat by burning fuel, a geothermal system simply moves heat from one place to another. It uses the stable underground temperatures to heat your home in winter and cool it in summer.
Talk to a Geothermal ExpertSo let’s dive deeper to understand how geothermal heating and cooling work, the key components involved, and what happens during both heating and cooling modes.
While outdoor temperatures can swing dramatically throughout the year, the temperature below the frost line remains stable. In most parts of Ontario and across much of Canada, the underground temperature ranges from roughly 2°C to 8°C, depending on location and depth. This stability is what makes geothermal systems so efficient. In winter, the ground is much warmer than the outdoor air, providing a reliable source of heat. In summer, it’s much cooler than the air outside, making it an ideal place to release unwanted heat from your home. A geothermal system exploits this natural temperature difference by using the ground as a heat source in winter and a heat sink in summer. 
In winter, the system’s main job is to collect natural heat from the ground. A fluid moves through the buried ground loop and absorbs stable thermal energy of roughly 2°C to 8°C from the soil. This fluid then carries the heat inside to the heat pump. Once the heat reaches the indoor unit, it raises the temperature and spreads it throughout your home.
The key point here is that the system isn’t generating heat by burning anything. It collects heat already in the soil and concentrates it for use in your home. That’s why geothermal heating uses so much less energy than a furnace: it moves heat rather than creates it.
But what about really cold days? In heating mode, a geothermal system draws heat from the ground rather than the outdoor air, so its performance is far less affected by extreme weather than that of an air-source heat pump. No matter how cold it gets outside, the ground remains a reliable source of heat.
In summer, the entire process runs in reverse, and it’s just as effective. Instead of acting as a heat source, the earth becomes a massive “heat sink.” The system pulls unwanted heat from your indoor air and pumps it into the much cooler ground. The key to this process is a small part inside the heat pump called a reversing valve. This valve controls the flow in the heating and cooling cycles, allowing the same equipment to efficiently provide both heating and air conditioning.
In cooling mode, your home produces internal heat gains in the summer, which gets stored in the ground around the loop. This slight warming of the soil helps prepare it for the next winter by recharging its ability to provide heat. Running the same loop throughout the year offers this added benefit.
The ground loop is the vital physical link between your home and the earth. It acts as a massive, underground heat exchanger. A liquid mixture (usually water and an eco-friendly antifreeze) constantly circulates through this network of pipes. Without the ground loop, the system would have no way to access the earth’s stable energy. Ground loops are made from high-density polyethylene (HDPE) pipe, the same material used in municipal water mains. It’s flexible, corrosion-resistant, and can last up to 50 years or more underground without degradation. The type of loop depends on your property size, soil conditions, and whether a suitable water source is available. 
All three configurations are closed-loop systems, meaning the fluid remains sealed inside the piping and never contacts the surrounding soil or water. An alternative is an open-loop system, which draws groundwater directly from a well. It can be highly efficient but depends on water quality, flow rates, and local regulations.
The ground loop delivers heat energy to the indoor heat pump unit, which concentrates it and delivers it to your living space. So, how does a geothermal system work
Here’s the full cycle:
Step 1
The fluid that loops through your yard returns inside, carrying the heat it just absorbed from the ground. In winter, it might return at around 2–8°C, which sounds cold in absolute terms, but is much warmer than the outdoor air and carries enough thermal energy to run the heating cycle efficiently.
Step 2
Inside the heat pump unit, the warm fluid passes through a heat exchanger called the evaporator. On the other side is a refrigerant, a substance that changes between liquid and gas states at low temperatures. The heat from the fluid causes the refrigerant to evaporate into a low-pressure gas.
The fluid gives up its heat to the refrigerant, then loops back outside to collect more from the ground.
Step 3
This is the most essential step. The newly formed refrigerant gas enters the compressor, which tightly squeezes the vapour. This is the only part of the process that requires a meaningful amount of electricity.
However, because you are using electricity just to squeeze heat that already exists, rather than burning fuel to create new heat, the system remains incredibly efficient.
Step 4
So, the refrigerant is now a super-heated gas, and it passes through a second heat exchanger, where it releases this intense heat into your home, either warming the air that blows through your vents or heating the water for your floor pipes.
As the heat leaves the refrigerant and enters your rooms, it cools and condenses back into a liquid. It passes through a valve that lowers its pressure, cooling it again, and then gets ready to repeat the entire cycle.
Professional heat pump installation ensures efficient heating and cooling for your home, improving comfort and energy savings year-round.
