What Is a Heat Pump & How Do They Work? (Systems Explained)

As technology continues to improve, HVAC engineers are finding new ways to make home climate control more affordable and efficient. Heat pumps are one of the latest system types to grow with this new technology.

With machines reaching over 40 SEER in testing labs, the currently available units are well over 20 SEER in most cases. This alone makes heat pumps one of the most efficient systems available. Let’s take a look at the heat pump to find out how they work and if they are right for you and your home.

What is a Heat Pump? (& The Main Parts)

The heat pump technology was first introduced as a practical application in the early 1940s. An Englishman named John Summer built a recirculating heat pump using antifreeze in Norwich, England. Before that, Peter von Rittinger discovered the heat pump properties trying to dry out brine salt in 1857.

This same technology is used today, and in residential heating and cooling, it has exploded as one of the most efficient heating and cooling systems on the market.

A heat pump (also known as a mini-split system) uses electricity and refrigerant to remove heat from the air to cool a home or reverses the pump to remove cold air from the home to raise the temperature.

On a small scale, it works much the same as a central air system by absorbing heat into the coils of refrigerant and moving that heat to another area. In the summer, the heat is moved outside, keeping the home cooler. In the winter, the heat is brought inside to warm the home.

If you are familiar with central heating and air, some of the components may look familiar.


The compressor sits in the condensing unit outside the home. It is the heart of the system, continuously pumping refrigerant through the refrigerant lines to and from the wall cassette mounted indoors.

The compressor’s job is to take the refrigerant passing through and compress it. This raises the heat and pressure of the refrigerant, allowing the rest of the system to distribute that heat as needed.


The condenser houses the compressor and condenser fan. Its primary job is to move air from outside the home over the refrigerant coils. In heating mode, it pulls the warmer air from outside, raising the temperature of the refrigerant, which is then pushed to the evaporator inside, and warm air enters the home.

In cooling mode, the condenser pulls the air outside over the coils, removing the heat from the refrigerant and returning it to the evaporator to help cool the home.


The evaporator is housed inside the wall cassette on your wall. It functions much the same way as a central air evaporator. The coils inside are cooled where the air is passed over them. In the winter, cold air from the home is pulled in and moved to the refrigerant, where it is expelled outside.

In the summer, the warm air from the home is passed over the coils where it is chilled and pushed back into the room, dropping the interior temperature.

Air Handler

Unlike most of the other parts of the system, the air handler has a single job. It is designed to pull air in from the room, pass it through the evaporator coils, and then take the heated or cooled air and move it back into the room.

Reversing Valve

The reversing valve is a check valve on the system lines that controls the directional flow of the compressor. In cooling mode, the refrigerant moves in one direction, sending cold refrigerant to the evaporator.

In heating mode, the valve switches directions, forcing the compressor to run backward, pulling the hot refrigerant from the evaporator, and sending hot refrigerant to the evaporator so it can warm the air inside.

How Does a Heat Pump Work? 5 Different Types Explained

There are different types of heat pumps, and each one works slightly differently. For example, some types are much better in colder weather, and some don’t rely on the air temperature. Let’s take a look at the various types of heat pumps to figure out which one best suits your needs.

Air Source Heat Pump System

Heat pumps can be designated by many different aspects. The most common is by how the system is installed. Air source systems are the most common. They consist of an external condensing unit and pump with an interior evaporator and air handler.

The process works much the same as a central air conditioner. The compressor pressurizes the refrigerant, which is passed through the evaporator, where the air is cooled. In winter, the valve reverses, and the warmth is moved to the evaporator, where it heats the air. This system is also referred to as an air-to-air heat pump.

Ground Source Heat Pump System

Ground source heat pumps use a closed-loop system of piping. Inside the pipes is a mixture of water and antifreeze. As the pump circulates the water mix, it absorbs the heat from the ground around the pipes, moving it through the system where the heat is then transferred to the home.

Also known as ground to air or water to air, these systems are common, but can get confusing. Water source heat pumps (explained below) use water differently and create confusion when talking about styles.

The main difference to keep in mind is that the ground source system (installed vertically or horizontally) uses the ambient temperature of the ground to add or remove heat. Water source systems use the temperature of the water.

Water Source Heat Pump System

A water source heat pump uses two different heating and cooling methods. The most common is called a water to water system. This is a closed-loop system, much like a ground source heat pump. Except instead of being buried, the water mix pipes are submerged in water (lake, river, etc.).

The second type is known as an open-loop system heat pump. Instead of using water and antifreeze mix in pipes, water is pumped directly from a source (generally an aquifer), where it is passed to the pump and through the system. On occasion, the water passes through a heat exchanger before entering the system to raise the temp of the water.

Water Loop Heat Pump System

A water loop system is almost identical to a closed-loop water source heat pump. Both use closed-loop piping filled with water or antifreeze to move through the system. The difference here is that a water loop system, unlike a water source system, is heated.

Various methods are used to heat the water, but the most common are electric heat exchangers and natural gas furnaces.

Exhaust Air System

An exhaust air heat pump is the least common application but maybe the most efficient. It relies on the heated exhaust air of other appliances or systems to heat the water in pipes before that exhaust is moved back to the atmosphere.

These systems don’t need to heat or cool the water or the air and rely on other external sources, making them extremely low energy consuming devices with a relatively high efficiency output.

Cooling Mode

In cooling mode, a heat pump works very similarly to any other refrigerant-based air conditioner. The biggest difference is the reversing valve. When the valve is in the vertical position, refrigerant flows from condensing unit (outdoors) to the evaporator unit (indoors). Let’s look at the actual process.

  1. .The refrigerant is a heated, low pressure gas. It enters the reversing valve and is pushed to the compressor.
  2. .The compressor condenses the gas as it is passed through the coils of the condensing unit.
  3. .The condenser fan moves external air over the coils, which is cooler than the coils’ refrigerant. The sudden change in temperature causes the refrigerant to cool rapidly, and the liquid starts the expansion back into a gas as it passes through the expansion valve.
  4. .The cold gas is then sent through the evaporator unit, where the air handler pulls air from inside the home to pass over the evaporator coils.
  5. .The warm air passes the warmth and humidity to the coils, which drops the air temperature before it is sent back into the room.
  6. .As the temperature indoors cools, the cycle repeats. Once the set temperature is reached, the system shuts off until the indoor temp rises above the setting once again.
Heating Mode

When you set the heat pump to heating mode, the only physical change is the reversing valve. The valve rotates 90 degrees (to a horizontal position) which causes the system to move the refrigerant through in the opposite direction.

  1. .Cold refrigerant gas is moved through the reversing valve from the condenser to the compressor. The compressor compresses the gas into a high pressure, heated liquid, where it is then sent to the evaporator unit.
  2. .The refrigerant passes the heat to the air brought in by the air handler. The heated air is blown into the room, raising the temperature. Meanwhile, the refrigerant cools and begins to expand into a low pressure gas.
  3. .The gas slows and is forced through the expansion valve, where it cools even more.
  4. .As the gas passes through the condenser coils, the condenser fan pulls warmer external air through the coils, where another heat exchange takes place. The heat is added to the refrigerant from the air, and the colder air is pushed outdoors.
  5. .The refrigerant passes through the compressor, where the system begins again. Once the set temperature is reached, the system will shut down until the indoor temperature drops too low once again.

4 Main Benefits of Installing a Heat Pump

We already know that heat pumps are among the leaders when it comes to efficiency. This fact, along with multiple other benefits, makes upgrading to a heat pump a worthwhile investment. For new construction, HVAC upgrades, or updating your home, a heat pump is a solid option.

  • Increased efficiency with lower energy costs.
    If your current system is over 10 years old or less than 14 SEER (or even both), it is time for an upgrade. Heat pumps generally range between 18 and 22 SEER and cost less to operate than a standard furnace.
  • Acts as both a heater and AC.
    A mini-split system reverses the pump and compressor, allowing you to heat and cool your home using the same unit. This saves energy costs and doesn’t require multiple components or systems to be installed.
  • Much safer than an open fire.
    When it comes to home heating, many options require combustible gases that are not only a fire hazard but can also leak carbon monoxide. Heat pumps only use electricity for power and refrigerant in a sealed system for heating and cooling.
  • Long lifespan.
    When properly installed, maintained and cared for, a new heat pump can easily last over 20 years. Compared to the 10 – 15 year expectancy of a modern central air system, it makes economic sense on all levels.

It is also worth noting that many heat pumps are quite affordable. However, while they can be cheaper than many other home climate control options, they aren’t exactly cheap. If you need financing, we may be able to help. Check out our HVAC financing guide for information.

The fundamental principle of working – Heat Pump

5 Tips to Keep Your Heat Pumps Electricity Consumption Down

As a whole, heat pumps are highly economical, provide great value, and consume less electricity than other home climate control systems. As the temperature outside drops, they do tend to lose some of that efficiency, though.

However, don’t let that dissuade your decision. A heat pump is generally efficient and highly effective down to about 25 degrees (Fahrenheit). Some models start to work harder and consume more electricity once the temperatures dip below about 40 degrees.

There are things you can do (depending on the type of heat pump system you have) to help maintain efficiency and continue to save money by using heat pumps.

Avoid varying the temperature during the day.

Constantly changing the thermostat is a great way to lose any efficiency you have. Once you have the thermostat set, you should leave it. If you need to make changes, you don’t want to fluctuate more than about 1 degree every two hours.

Restrict the flow temperature of the heating water.

For water to air systems, many installers will set the flow temperature of the water to much higher than you need. Reducing the water temperature will reduce the time and frequency the electric heaters need to come on to maintain water temp.

Manually activate the electric heater.

Some models come with a supplemental electric heater that will come on when the heat pump isn’t producing enough heat. Many homeowners connect this system to the thermostat and let it come on as needed. However, using a manual control option will let you have more specific control over the time and frequency of the electric heat source.

Regularly maintain your system.

Maintenance and cleaning will go a long way to keeping your heat pump performing at its best. For optimal performance, keep airflow moving by changing air filters on time and regularly cleaning the coils and vents to keep the system free of dust and debris build-up.

Combine your heat pump with solar panels.

While solar panels are a costly initial install, they can drastically reduce the amount of electricity you need. If you have an existing solar panel system, connecting your heat pump can drop electric use to near-zero. If you decide to install a solar-powered system after the fact, you can recoup costs much quicker using a heat pump.

Heat Pump Maintenance Tips

When it comes to cleaning and maintenance, heat pumps are fairly low maintenance. While you may not spend as much time keeping your system operational, there are still requirements you should follow.

There are two different maintenance types to consider, DIY maintenance done by you and professional maintenance performed by an HVAC professional.

DIY maintenance

Homeowner maintenance is relatively routine and simple. Most heat pumps don’t require a lot of excess cleaning and repairs. However, it is in your best interest to perform the following attributes.

  • Replace filters regularly. A dirty filter impedes airflow and makes the system less efficient.
  • Clean coils. Twice a year, you should clean the condenser unit and coils and inspect the evaporator coils, cleaning as needed.
  • Clean the wall cassette. Dust and debris build up on the vents and casing of the wall unit lowers air quality and can alter the air handler’s heating and cooling ability.
  • Check lines and connections. Once a year, you should inspect the refrigerant lines and power connections to ensure there isn’t any damage, bending, or loose connections.
  • Check the thermostat. Loose connections, bad batteries (if equipped), and other issues with a thermostat can drastically affect the performance of the heat pump.
Professional Maintenance

Hiring an HVAC tech once a year to inspect your system will go a long way to maintaining performance and keeping costs down. A standard inspection consists of the following aspects and should last about 2 hours.

  • Check entire system for dirt and debris accumulation.
  • Inspect ducts (if equipped) for damage and repair as needed.
  • Test airflow to and from air handler.
  • Check refrigerant levels and recharge as needed.
  • Inspect refrigerant lines and test for leaks.
  • Lubricate and inspect bearings, motors, and belts.
  • Test thermostat and electrical lock outmodes.
  • Clean condensing unit and drain pan drain holes or lines.

People Also Ask (FAQ)

Is a heat pump gas or electric?

While some water source heat pumps are heated by natural gas, the rest of the system and all other heat pumps are electric powered. The gas heated water units are known as gas-fired heat pumps, they are also efficient, but the accumulated ammonia is not condensed through the compressor and is instead evaporated into the water itself.

Is it true that heat pumps stop working when it gets very cold out?

Unless the entire system freezes up, a heat pump won’t stop working. However, at lower temperatures, the heat pump will become less effective and less efficient. At about 40 degrees (Fahrenheit), most heat pumps will begin to lose efficiency. At 25 and below, they stop producing enough heat to make much of a difference. However, as a supplemental heat source, they will continue to move heated air through the home as long as it is available.

Can I heat my home with heat pumps without any other heat source?

Depending on where you live, average ambient temperatures in winter and humidity levels, it is possible to use only a heat pump to warm your home. However, even named a heat pump, the units were originally designed as a supplemental heat source. In general use in most regions, heat pumps will need assistance from electric heaters, gas furnaces, or even pellet stoves when temperatures drop too low.

What is a heat pump water heater?

A heat pump water heater (HPWH), also known as a hybrid water heater, uses heat pump technology to raise the water temperature in a tank, using refrigerant and ambient air to raise the water temperature, which is then moved to the faucets of the home.

Who makes the best heat pump system?

Many brands make heat pumps, and the top names in HVAC are still the leading names when it comes to heat pump systems. Mini-split systems, both ducted and ductless, are great from companies like Trane, Carrier, Lennox, Rheem, and Goodman.

What are the disadvantages of a heat pump?

There aren’t many downsides to heat pump systems. However, some brands can be quite expensive upfront, and installation is best left to a professional. Even with DIY install possibilities, many brands will void a warranty if it isn’t installed professionally. The only other downside is that in extremely cold climates, heat pumps may require additional heat sources to maintain your home’s temperature.


Heat pumps are among the most energy efficient HVAC systems available. While they may have a higher installation cost or initial purchase costs, they make up for it in the long run. Compared to traditional central air systems, mini-split heat pumps are over twice as energy-efficient. Because of this, systems pay for themselves in your monthly energy savings.

By being more efficient and better suited to heat and cool the home, they make an excellent upgrade over older central air units. Now that you know how they work and what components go into keeping your home comfortable, you may be more inclined to make a purchase. If so, owning a heat pump will not be a disappointment or regret.

Josh Mitchell

Josh Mitchell

My name is Josh and I am obsessed with DIY and improving my family home. HVAC topics can be tricky for homeowners so I decided to share my knowledge on the subject. When I am not working on DIY projects, you can find me at the beach or my local coffee shop.