how do air source heat pumps work

How do heat pumps work?

Heat pumps work by distributing heat from one space to another, serving as energy-efficient heating and cooling systems. Unlike conventional HVAC systems, heat pumps can transfer heat both ways – from outside to inside to heat, and from inside to outside to cool. Diverse and advanced heat pump technology creates solutions to fit any home’s needs and budget, and in this article, we explain how heat pumps work in all seasons and the advantages they offer.

Key takeaways

  • Heat pumps distribute heat from one space to another to provide energy-efficient heating and cooling with one system.
  • As a heating system, heat pumps draw heat from the outside air and move it inside; as a cooling system, they remove heat from the air inside a home and move it outside. 
  • Heat pumps consist of outdoor and indoor units and include refrigerant, a compressor, reversing valve, and expansion valve. 
  • There are various types of heat pumps: air source heat pumps pull heat from outside air whereas ground source or geothermal heat pumps work with heat from the ground. Additionally, a heat pump system can be both ducted or ductless (mini splits). 
  • Heat pumps can be powered by solar panels to generate totally emission-free heating and cooling for your home. Use the EnergySage Marketplace to connect with pre-screened installers and receive solar quotes today!

What’s in this article?

How heat pumps work as a heating system

Unlike furnaces, heat pumps don’t burn any fossil fuels to generate heat and require less energy to operate. Simply put, heat pumps extract heat from outside – either from the ground or from the air – and transfer it to your home or building. We’ll specifically explain how an air source heat pump works in the winter, but it’s important to note that air source and ground source heat pumps function in virtually the same way:

First, the fan draws outside air into the outside unit. The air then flows over the heat exchanger – a tube with refrigerant fluid pumped through it – where it warms the refrigerant fluid. The heat causes the liquid refrigerant to evaporate and the vapor is compressed to concentrate the absorbed heat. As your home warms up, the vapor cools and is pumped back through the first heat exchanger to collect more heat energy from the outside air. This process repeats to maintain your preferred air temperature. 

How heat pumps work as a cooling system 

In warmer months, this process simply runs in the opposite direction to cool your home. Instead of transferring the heat from the outside air to inside, the refrigerant is pumped through a heat exchanger inside your home first, where it absorbs heat energy and moves it outside. Put another way, heat pumps as cooling systems work in the same way as an air conditioner; they release the heat from inside your home to the outside air. 

Components of a heat pump

Heat pumps include an outdoor unit and an indoor unit; the systems also have a refrigerant, a compressor, a reversing valve, and an expansion valve.

Outdoor unit

The outdoor unit is the heat exchanger. The fan blows outside air over the coil, and then the coil operates as a condenser when cooling or an evaporator when heating.

Indoor unit

The indoor unit is the air handler. The fan moves air across the coil and through the ducts. The coil acts either as an evaporator for cooling or a condenser for heating. The indoor unit is largely dependent on the type of heat pump; you may have multiple air handlers inside, or mini splits if you aren’t using ducts.


The refrigerant is the substance that actually flows through the heat pump system via piping, absorbing and rejecting heat as it circulates.


The compressor is the component that pressurizes the refrigerant and moves it through the system. 

Reversing valve

The reversing valve reverses the flow of refrigerant, allowing the system to operate in the opposite direction and switch between heating and cooling.

Expansion valve

The expansion valve regulates the flow of the refrigerant as it passes through the system, allowing for a reduction of pressure and temperature of the refrigerant.

Types of heat pumps

With various makes, models, and types, heat pumps are highly customizable. Heat pump technology continues to evolve and advance, but the most common types of heat pumps today are air source and ground source heat pumps. 

Air source heat pumps

The most common type of heat pump on the market today is the air source heat pump. As previously mentioned, air source heat pumps use outside air to regulate the temperature of a home or building. Air source heat pumps are less expensive to install compared to geothermal heat pumps but are less efficient due to the higher temperature variance of outside air. 

Mini splits

Mini splits are a type of ductless air source heat pump. Rather than transferring air through ducts, mini splits pump air directly into the intended space through individual indoor units. Mini splits offer greater flexibility and are more efficient than ducted systems because of the direct airflow. 

Ground source or geothermal heat pumps

Instead of pulling outside air, ground source or geothermal heat pumps absorb heat from the ground and transfer it indoors. Although they cost more to install, the temperature stability of the ground usually translates to lower operating costs for geothermal heat pumps. 

Heat pumps vs. traditional HVAC systems

The biggest difference between heat pumps and conventional HVAC is their ability to heat and cool, whereas furnaces can only heat and air conditioners can only cool. As a cooling system, heat pumps and air conditioners operate in the same way, have comparable energy efficiency ratings, and come at similar prices. But as we mentioned, an air conditioner must be paired with another heating system that comes with additional costs and maintenance requirements. 

Conversely, heat pumps and furnaces have little in common. For starters, heat pumps transfer heat instead of generating heat like furnaces. This not only significantly reduces the amount of energy required to heat a space, but also avoids burning fossil fuels. The Department of Energy reports that air-source heat pumps can reduce electricity use for heating by 50 percent compared to other electric heating options. Overall, heat pumps can provide savings of $500 to $900 annually. Depending on your home and local energy rates, however, gas furnaces may benefit from lower natural gas rates. Additionally, the lifetime of a furnace currently tends to be a bit longer than that of a heat pump. 

Pair your heat pumps with emission-free solar panels

Heat pumps pair naturally with solar panels to offer energy efficiency, savings, and emission-free heating and cooling for your home. Connect with pre-screened installers in your area on the EnergySage Marketplace to receive solar quotes today! Just leave a note to let installers know you’re interested in heat pumps, too. Still have questions? When you sign up for the Marketplace, we’ll connect you with an Energy Advisor from our team (free of charge) to help guide you through every step of the way.

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