What Is a Heat Pump's Refrigeration Cycle?

By Sarah Stasik

November 09, 2025

The heat pump refrigeration cycle enables a heat pump to remove hot air from a room during the summer and bring in warm air from outside during the winter. Heating your house by pulling in warm air may seem crazy when it's 38 degrees Fahrenheit (3 degrees Celsius) outside, but once you understand the basics of the refrigeration cycle, it begins to make more sense.

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You probably already know the overall physics behind the process, aka the laws of thermodynamics. They include facts like:

Heat moves on its own, typically from higher temps to lower.
In any system involving temperature, components will try to reach stasis — where the temperature is even across the whole system.

Consider a bathtub full of water. If you fill it with water that's too hot, you can add cold water. At first, you'll feel the cold water on the far end of the tub, but eventually — even if you don't stir it — all the water becomes the same temperature. Long enough and the temperature of the water becomes similar to the temperature of the air in the bathroom, too.

This is similar to how heat pump refrigeration cycles work.

What Is a Heat Pump Refrigeration Cycle?

The refrigeration cycle is the movement of refrigerant through the components of a heat pump system. The refrigerant moves through the main parts of the system, including the:

Compressor
Condenser
Expansion valve
Evaporator

When the refrigerant makes a loop through all the components and returns to the start, having heated and then cooled, a refrigeration cycle is complete.

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How Does the Refrigeration Cycle Work?

Your heat pump system uses refrigerant to move heat through the system, helping warm or cool the air in your home. Here's how it works.

Compression

At this stage, the refrigerant is in gas form because it's warm. The compressor begins to squeeze the gas, transferring energy into the gas and making it hotter.

Condensation

As the gas becomes hotter and more pressured, it moves into the condenser coil. Here, it starts to release heat energy. The air around the coil isn't as warm as the gas, so the heat moves into it — remember, the system is trying to reach stasis, where the same temperature is found throughout.

The refrigerant gas cools as this occurs and turns back into a liquid. What happens next depends on whether you're heating or cooling your home. If you're heating your home, the warm air produced by this process is forced into your home. If you're cooling your home, the warm air is transferred outside your house.

Pressure Drop

Before the refrigerant can pick up new heat to restart the cycle, it must cool down fully. It passes through the expansion valve, which forces a rapid drop in pressure. This makes the refrigerant colder — it's similar to when you spray compressed air out of a can and it feels very cold.

Expansion

Next, the liquid refrigerant goes through the evaporator coil. Here, it starts to pick up ambient heat. When cooling, it draws heat from inside your home. When heating, it picks up heat from outside. Even if the air feels cold to you outside, it or the ground has enough thermal energy to help warm the refrigerant.

The warming refrigerant turns back into a gas, and the cycle starts again.

Caring for Your Heat Pump

This simplified look at how a heat pump works and the energy transfer that's required to heat and cool your space helps explain why every component is critical. You can support efficient heat pump operation by investing in regular maintenance and inspections, ensuring your heat pump is the right type and size for your home and setting your thermostat at a steady, reasonable temperature.

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