What Is a Heat Pump and How Does It Work?

Mariel Loveland
Written by Mariel Loveland
Updated September 21, 2022
couple at home relaxing
Photo: Cavan Images / Adobe Stock


  • Heat pumps warm or cool your home through heat transfer, similar to AC.

  • They don’t create original heat like a standard furnace.

  • They can use air, the ground, or water to transfer heat.

  • A new system can lower your carbon footprint by up to 54%.

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You've heard the term, but what is a heat pump, and how does it work? Despite its name, this system can cool down your house just as much as it heats it. Either way, it's an energy-efficient alternative to a traditional HVAC system. Is a heat pump right for your home? This guide sheds light on how heat pumps work and how they benefit homeowners.

What Is a Heat Pump System for a House?

A heat pump system is a type of home heating and cooling system. It doesn’t create heat like a traditional furnace. Instead, it uses a refrigerant to transfer heat from the air (or, less commonly, the ground or water). In this sense, it’s similar to an air conditioner, but it can reverse the process to warm your home. Overall, these systems are a great way to increase your home’s energy efficiency and lower your carbon footprint because, unlike a traditional HVAC system, they run on electricity rather than fossil fuels.

Heat Pump Parts

To understand how a heat pump works, you need to understand the key parts of heat pump technology. These parts work to either transfer heat or change the pressure (and thus temperature) of the refrigerant, resulting in either a cooling or heating process. 

  • Indoor unit: This is where heat transfers between the inside air and refrigerant. This unit contains a fan and a coil. The fan circulates conditioned air through your home. The coil acts as either an evaporator (if you’re cooling your house) or a condenser (if you’re heating your house).

  • Outdoor unit: This is where heat transfers between the outside air and refrigerant. The unit contains a fan and a refrigerant coil that acts as a condenser (for cooling) or an evaporator (for heating). 

  • Compressor: Similar to an air conditioner compressor, this pressurizes and heats the refrigerant.

  • Expansion valve: This depressurizes and cools the refrigerant.

  • Reversing valve: This reverses the cycle, allowing you to switch between heating and cooling your home.

How Does a Heat Pump Work?

Heat pumps have two different processes for heating and cooling. These cycles are essentially a mirror image of one another. Let’s break it down.

The Cooling Process

During the summer, your heat pump will use refrigerant to cool your home. This refrigerant will cycle through the different parts of the system, changing pressure and temperature. Here’s how it works:

  1. Starting at the indoor unit: warm indoor air will pass over a cool refrigerant coil. The cool liquid refrigerant inside the coil will absorb the air’s heat and evaporate into a low-temperature gas. Your system will then circulate the newly cooled air through your home while the refrigerant travels through the rest of the system.

  2. Moving to the compressor: The gas refrigerant moves to the compressor, where it’s heated and pressurized.

  3. Moving to the outdoor unit: The gas passes over the outdoor coil, where it transfers heat to the outdoor air. The warmed air is blown back outside, away from your home. At the same time, the refrigerant condenses back into a liquid.

  4. Passing through the expansion valve: The expansion valve cools the liquid refrigerant as it depressurizes. This refrigerant then cycles back to the indoor coil, where the process starts again.

The Heating Process

To heat your home, your heat pump will reverse the cooling process.

  1. Starting at the indoor unit: Cool indoor air will pass over a coil filled with warm, high-pressure refrigerant gas. The gas will transfer heat to the air as it condenses into a liquid. The newly warmed air is then circulated throughout your home

  2. Passing through the expansion valve: The liquid refrigerant moves through the expansion valve and cools down as it’s depressurized.

  3. Moving to the outdoor unit: The liquid refrigerant moves to the outdoor coil, where it absorbs heat from the outside air (yes, even cold air has some heat).

  4. Moving to the compressor: The compressor pressurizes and heats the refrigerant. This high-temperature, high-pressure refrigerant is then sent back inside your home to start the process again.

Types of Heat Pumps

While many hybrids and combination heat pump systems are available, the three main heat pump systems are air-source, water-source, and ground-source systems. Here's a brief overview of each of these systems.

Air-Source Heat Pump System

You may be surprised to find that, even on a cold day, your air-source heat pump can take in heat energy from the outside air and transfer it into your house to warm you. The refrigerant absorbs the heat, while the pump pushes the hot air through your home through a loop system. The opposite happens in the summer; your air-source system pulls hot air from inside your home and releases it outside in hotter weather.

Water-Source Heat Pump System

A water-source heat pump works just like the air-source pump (and a ground-source pump, too, as you’ll see). The main difference is that water-source heat pumps use a piped water cycling system to transfer heat to and from your home. 

Ground-Source Heat Pump System

Your ground-source pump, also known as a geothermal heat pump system, pulls heat from the ground into your home in the winter. The ground-source pump cools the air in the summer and makes it easier for your AC to maintain cooler temperatures. 

Benefits of Heat Pumps

Nothing quite spells out the benefits of a heat pump like a list, so here’s what your new heat pump system can do to benefit you:

Is a Heat Pump Right for Your Home?

Heat pumps for heating and cooling can struggle in cold weather, but there’s actually a heat pump system for every home. If you live in a cooler climate, you can install a dual-fuel HVAC system, which pairs a furnace with a heat pump. When temperatures drop to the point where electricity is no longer economical, you can use your regular natural gas furnace.

Regardless, heat pumps are still one of the most affordable and efficient ways to heat and cool your home. Ductless varieties are sometimes one of the only solutions for homeowners who don’t have existing ductwork (or want to save the thousands it costs to install ducts). A heat pump installer near you can help you find the best heat pump system for your home.

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