What is a Heat Pump

Heat pumps are having a bit of a moment right now, and for good reason: they can replace your furnace and your air conditioner, they can drastically cut both your heating and cooling bills, and they don’t burn fossil fuels.

But what is a heat pump in a house and how do heat pumps work? In this post, we’ll tackle those questions while also explaining different types of heat pumps, how to install them, how a heat pump performs its cooling function and its heating function, and how homeowners can get tax credits for converting to a heat pump. Finally, we’ll answer any remaining questions about heat pumps, and detail how heat pumps can help the environment.

Let’s flip the switch, and transform some information into knowledge.

How does a heat pump work?

Heat pumps, like the name suggests, are all about the transfer of heat. They can push heat out of a house to cool the residence, and they can pull heat into a home to warm it. They use electricity and a refrigerant—similar to what you’ll find in an air conditioner—to perform both functions.   

How does a heat pump work: Cooling mode

In cooling mode, the heat pump relies on a scientific property of heat energy, which is that warm air tends to seek cooler areas with lower pressure. The pump facilitates this process, placing warm air in contact with cool air and lower pressure, where Mother Nature takes over, transferring the heat.

Here’s the blow-by-blow of how a heat pump works in cooling mode:

1. Liquid refrigerant fills the heat pump’s indoor coil. Warm air from inside the house is blown across the coils, where it is absorbed by the refrigerant and cooled. That air is then distributed through the ducts in the home. Having absorbed the warm air, the liquid refrigerant has heated up and evaporated into gas form.
2. The gaseous refrigerant then passes through a compressor, where it gets pressurized and, as a result, warmed up even more. The hot, pressurized refrigerant then flows to the heat pump’s outdoor coils.
3. A fan in the unit’s outdoor side pushes exterior air across the coils. This cooler air hits the hot refrigerant in the outdoor coils, transferring the heat to the outside air. The refrigerant then cools, returns to a liquid state, and gets pumped back to the expansion valve on the indoor side of the unit. 
4. The expansion valve performs the opposite function of the compressor, reducing the pressure in the liquid refrigerant and cooling it back to its original temperature. Now the refrigerant can be pumped back into the unit’s indoor coil to restart the cycle.

How does a heat pump work: Heating mode

To warm your home, the heat pump executes the same process, except that the flow of refrigerant is reversed. The unit features a reversing valve, which sends the refrigerant in the opposite direction and turns the outside air into the heat source, and the interior of the home into the place where the heat energy is released. In this mode, the outdoor coil becomes the evaporator (transforming the refrigerant into gas) and the indoor coil acts as the condenser (returning the gas to liquid state). 

Everything else remains the same: Liquid refrigerant fills the outdoor coils, where it absorbs warm air (even on cold days) and converts it into cold gas. That gas then gets pressurized, heated up, and pumped into the indoor coils. Air inside the home hits the hot gas, cooling it, and becoming warmer itself in the process. The gas returns to a liquid state, then gets depressurized before returning to the outside unit as a cool liquid and beginning the cycle again. 

What is a heat pump system: Heat pump basics

As mentioned, a heat pump doesn’t actually generate heat, but transfers warm air from the exterior of a building to the interior, or vice-versa, depending on which mode it’s in. In cooling mode, the unit functions like an air conditioner, pulling warm air from inside the house, cooling it, and releasing heat energy to the exterior. The reverse occurs in heating mode, when the unit extracts warm air from outside and releases its heat energy into the home.

Heat pumps don’t use fossil fuels and can replace both a furnace and an air conditioner. They also use less energy than furnaces or air conditioners, so they can cut costs on your heating and cooling bills. Learn more about how to cut your power bill costs with energy efficient habits and environmentally friendly appliances like an electric hot water heater.

Heat pumps are most prevalent in the Southeastern US, where residential natural-gas connections are less common and the temperature rarely plunges below freezing, but they are becoming more widespread in other regions, especially now that much improved cold-climate heat pumps are emerging. Indeed, in 2022, US heat pump sales exceeded those of gas-powered furnaces for the first time ever. If you’re considering going with a heat pump system as a cost-cutting, environmentally friendly appliance, the main things to consider are the size of your residence, the quality of its insulation, and your local climate.

Heat pump system parts and components

Standard air-source heat pumps contain an outdoor unit and an indoor unit, which are connected. They both contain a coil and a fan. 

In cooling mode, the outdoor unit’s coil functions as a condenser; it switches to an evaporator in heating mode. The coil in the indoor unit works as an evaporator in cooling mode and as a condenser in heating mode. 

Other parts that make up a heat pump include:

Heat Pump Refrigerant

The chemical fluid that flows through the unit, extracting or repelling heat.

Heat Pump Compressor

Device that pressurizes the refrigerant, heating it up, as it circulates through the heat pump.

Heat Pump Expansion valve

Controls the flow of refrigerant and reduces the pressure, and in turn, temperature, of the chemical.

Heat Pump Reversing valve

This valve reverses the flow of the refrigerant and operation of the unit, allowing the heat pump to shift between its heating and cooling modes.

How does a heat pump work in winter

It seems counterintuitive that a heat pump would use exterior air to warm a home during the wintertime. Yet that is exactly what the unit does, since there is still heat energy to be found outside on cold days. In air-source heat pumps, the outdoor coils fill with cold refrigerant, which attracts warmth from the outside due to heat energy’s tendency to seek cooler temperatures. 

As heat pump technology improves, cold-climate heat pumps are getting better and better, with some models now able to function efficiently in single-digit Fahrenheit temperatures. 

If you make sure that your home is properly insulated and weather-sealed, pick the right equipment for the size of your house and the weather in your region, and, finally, select a contractor with a lot of experience in installing heat pumps, you will end up with an energy-saving, climate-friendly heat pump that cools and heats your home sufficiently no matter what the weather’s like outside.

What are different types of heat pumps

What is an air-source heat pump?

Air-source heat pumps are the most prevalent type of residential heat pump. In warm weather, they transfer warm air from inside a home to its exterior; in the cold season they extract heat from the air outside and release it into the home.

What is a ground-source heat pump?

A ground source heat pump harnesses energy from the sun, stored in the ground as heat.

What is a geothermal heat pump?

Geothermal heat pumps pull heat from the ground as well, but instead of using the sun, they derive their energy from the constant temperature below the surface, generated by the earth’s core.  

How does a geothermal heat pump work

The principles at work in a geothermal heat pump are identical to air-source units, the only difference being the location of the heat energy geothermal pumps use—namely, underground. To harness the constant temperature below the earth’s surface for both cooling and warming homes, geothermal heat pumps use a system of pipes or a ground loop that start inside the home and extend to the exterior, underground. Learn more about how geothermal energy can be used to power heat pumps.

Filled with refrigerant, or a combination of water, antifreeze, and refrigerant, these units absorb heat from the ground and transform it into cold gas, which gets pressurized, increasing its temperature, and pumped into the indoor pipes of the unit. The interior air contacts the hot gas, cooling it and becoming warmer in the process. The gas reverts to a liquid state, flows back to the exterior pipes where it undergoes depressurization in the expansion valve to cool even further, and starts the cycle anew.

The cooling process is the same, but runs in the opposite direction: the homeowner activates the reversing valve, and refrigerant starts on the inside, pulling heat from the home, transforming it, pressurizing it, and pumping it to the underground part of the circuit, where it is released as heat into the ground. The refrigerant then returns to liquid form, travels back to the interior part of the circuit, where it gets cooled further in the expansion valve, and is ready to start the process over.

Heat pump installation

So what is a heat pump HVAC and how do you install one? First, anyone installing a heat pump should have an expert’s grasp of not only electrical systems and wiring, but also heating, ventilation, and air conditioning (HVAC). Components that need to be evaluated include the size of the space and amount of energy required to heat and cool it; the optimal location for the heat pump on the property; the size and power of the heat pump; the layout of the ductwork; and the the unit’s compatibility with the electrical wiring in the residence. 

It’s a complex, detail-oriented job that must be done correctly to ensure the unit is as efficient, cost-saving and environmentally friendly as it can be.

How to install a heat pump

If you are among the most skillful, knowledgeable, and, most important, adventurous DIYers out there, you can install a heat pump on your own. Well, make that almost on your own. You’re more than likely going to need a pro to lend a hand at least once during the process. As mentioned, it’s a job that requires extensive knowledge of HVAC and electrical systems, and if not done right, it will undermine many of the benefits of the heat pump. It could also be a safety hazard. All of that said, there have been many daredevils who’ve taken on the task, and there’s no shortage of tutorials on the internet.

Heat pump tax credits

We’ve mentioned that heat pumps can save you money, increase the efficiency of your heating and cooling systems, and reduce pollution. They’re also a valuable tool in the effort to reduce climate change, because they produce zero harmful emissions. In addition to—and as a result of—all of these benefits, installing a heat pump in your primary home can qualify you for a tax credit. 

On January 1, 2023, homeowners became eligible to earn up to $3200 in tax credit for making qualified energy-efficient improvements to their main residences. 

You can earn up to $1200 for taking energy-efficient steps like weather sealing doors and windows, and up to $2,000 per year for installing a heat pump. The credit is available through 2032 for every year you make qualified improvements.

Heat pump FAQs

Are heat pumps loud?

Heat pumps generate a noise level on par with central air conditioning units. As refrigerant passes through the coils of the system a heat pump can sometimes emit a gurgling noise.

Will a heat pump increase the value of my home?

A 2020 study led by the University of Maryland’s Center for Global Sustainability found that the addition of a heat pump can add between 4.3% and 7.1% to the value of a home. To realize the full return on investment, though, the homeowner would need to have used a heat pump long enough to pay down the cost of purchase and installation.

Do heat pumps stop working when it gets very cold outside?

Cold weather can affect the efficiency of a heat pump, forcing the unit to work harder to produce sufficient warming output. But the mercury would have to plunge extremely low to cause a heat pump to completely stop working. Furthermore, cold-climate heat pump technology is rapidly improving. There are units now that can continue warming a house in sub-zero temperatures. These same heat pumps maintain peak efficiency down into single digit temperatures.  

How heat pumps help the environment

Heat pumps are one of the most environmentally friendly accessories you can add to your home. They don’t burn fossil fuels, they’re impressively efficient, and they can replace both your furnace and your air conditioner, cutting your heating and cooling costs in one fell swoop. Energy Star offers additional advice to learn more about how heat pumps save energy.

The fact that they run on electricity means they don’t emit any carbon while operating, and since heating and cooling residential and commercial buildings accounts for approximately 13% of US greenhouse gas emissions (per 2021 figures), widespread use of heat pumps could make a significant difference in the fight against climate change. Inspire Clean Energy offers energy plans with access to clean, renewable sources that can double down on the environmental benefits of heat pumps.