A heat pump doesn't generate heat; it transfers it from one place to another. It's an appliance with a bright future in an eco-conscious country.
If you aren’t familiar with heat pumps, there’s no time like the present to change that. California has announced it will begin phasing out gas furnaces in 2023, and because heat pumps use 50 percent less energy than electric resistance furnaces according to the Department of Energy, they’re poised to become the most economical heating option for Californians, as well as people in other states. Federal incentives designed to make purchasing and installing a heat pump system easier on the budget will soon expire, but you can still take advantage of them if you hurry.
So what is this home appliance that “pumps heat?” The idea isn’t exotic. Turn your window air conditioner around and it functions just like a heat pump, although an actual heat pump is a tad more sophisticated than this.
On This Page
What Is a Heat Pump System?
A heat pump is an electric appliance that transfers heat from outdoors to indoors, and vice versa.
Most heat pumps have reversing valves that allow them to also function as air conditioners. The main working parts are a compressor, which circulates a refrigerant through a system of copper coils, and a fan to circulate air into the living space.
Heat pump systems typically consist of two units, one outdoors and one indoors, connected by copper tubing that passes through the wall of the building. The compressor is usually outside.
How Does a Heat Pump System Work?
The refrigeration system consists of two coils (condenser and evaporator) separated by an expansion valve through which a refrigerant continuously circulates. In the condenser coil, the compressor pressurizes the refrigerant to condense it into a liquid. Because this process releases heat, the condenser coil is always hot.
The pressurized liquid presses against an expansion valve at the end of the coil. When the pressure is great enough, the valve opens and sprays the refrigerant into the evaporator coils, where the sudden pressure reduction turns the refrigerant into a vapor.
Vaporization draws energy from the surrounding medium (air, soil or water). This passes back into the condenser coil to be released as heat when the refrigerant re-pressurizes.
Types of Heat Pump Systems
It’s possible to categorize heat pumps according to the medium from which they exchange heat.
An air-source pump gets heat from the surrounding air. A ground-source (or geothermal) pump gets it from the ground, and a water-source pump from a nearby body of water. Ground- and water-source heat pumps utilize the stable temperature conditions found underground or in a body of water. They work better in cold climates than air-source models.
Another way to categorize heat pumps is by size. Whole-house units with powerful compressors can replace a furnace and air conditioner in a central heating/cooling system. The condenser coil is mounted in an air handler that also houses a blower.
Smaller heat pumps, known as ductless mini-splits, have one or more wall-mounted indoor units, each with its own fan. Mini-splits produce enough heat for a single room. There are also mini-split systems with a single compressor that feeds up to eight or nine wall-mounted units.
The environmental benefits of heat pumps
“Heat pumps don’t rely on fossil fuels for heating and cooling, so they are considered a greener solution than gas furnaces or traditional air conditioners,” says HVAC expert Brooke Greenwood.
“Because it taps into the year-round thermal energy stored in the ground, a geothermal heat pump is among the most energy-efficient, cost-effective home comfort systems available today.”
Kathy Hannun, who co-founded a geothermal heat pump company, elaborates: “Air-source heat pumps are a great improvement over gas or oil furnaces and can offer excellent efficiency in moderate climates. However, their performance can drop in very cold weather, whereas geothermal heat pumps maintain high efficiency regardless of outdoor temperature.”
Where Are Heat Pumps Most Common?
According to data from the National Association of Home Builders, 75% to 77% of homes in the East South Central and South Atlantic states have heat pumps, while 20% of homes in the West South Central states do. They aren’t as common in Northern states because air temperatures are too cold, and ground- or water-source models are expensive to install.
However, the situation isn’t static. Manufacturers are working to develop more efficient models that work in cold climates. Plus, units can be equipped with auxiliary resistive heaters to provide supplemental warmth on cold days.
Buying a Heat Pump
The most important characteristics to consider are the heat output, measured in British Thermal Units (Btus), and the Seasonal Energy Efficiency Rating (SEER). Heat output is also often measured in tons, where one ton = 12,000 Btus.
There are two rules of thumb for sizing a heat pump. One is to provide 30 Btus of heat per square foot of floor space. The other is to divide the total floor area by 500 to determine the number of tons you need. It’s important for an HVAC contractor to perform tests to accurately size a unit for a particular house so it produces the right amount of heat.
SEER numbers start at 13 (low efficiency) and climb to 21 or 22 (high efficiency). A unit with a high SEER number uses less electricity, but has more moving parts and costs more to buy and maintain.
In practice, a system with a 16 SEER should be adequate in moderate climates. To maximize performance in a colder climate or minimize power usage, go with a higher SEER. You can calculate the energy a particular unit uses and its monthly cost by dividing the heat output in Btus by the SEER. You’ll get the result in watts per hour. Then multiply that by the local electricity rate.
What about incentives?
Fewer energy incentives are available after Congress passed the budget bill of 2025, but Greenwood advises there are still incentives available for installing a heat pump. “You’ll want to act soon to ensure that you don’t miss out on some key savings. If you want to make sure you can make the most of these opportunities, here are some timelines to keep in mind:
- Section 25C (Energy Efficient Home Improvement Credit) and Section 25D (Residential Clean Energy Credit) will expire for projects placed into service after December 31, 2025.
- Section 45L (New Energy Efficient Home Credit) will expire for homes purchased after June 30, 2026.”
“Consumers,” says Greenwood, “can find a complete list of rebates and incentives available on Carrier’s website, and some utility companies run rebates for switching to an electric unit, so be sure to ask your local dealer about that as well.”
Installing a Heat Pump
Some mini-split units, like the Mr. Cool DIY, can be installed by homeowners. If you’re not comfortable with that, hire a licensed HVAC technician.
The outdoor unit mounts on a concrete pad or footers to keep it high and dry. One or more indoor units are installed on walls or inside an air handler connected to the building’s ductwork. The two units are then connected by refrigeration tubing and electrical wires that pass through the wall.
Because most heat pumps also function as air conditioners, a drainage tube is included for condensate that drips from the indoor coil when it’s cold.
Heat Pump Maintenance
Both the indoor and outdoor units need routine maintenance, including changing air filters and cleaning dust off the coils. The outdoor unit must be kept free of snow, leaves and other debris so air can circulate.
You may have to occasionally de-ice the evaporator coil in the outdoor unit in the winter and the indoor unit in the summer. Just turn off the power and let the ice melt, rather than trying to scrape it off and possibly damaging the coil.
FAQs
How long does a heat pump last?
Air-source heat pumps generally last 10 to 15 years, according to Hannun, but geothermal systems last much longer — typically 20 to 25 years for the indoor unit, and 50+ years for the ground loops. “The durability and lower maintenance needs of geothermal systems make them a strong long-term investment,” she says.
Do heat pumps need ducts?
Yes and no. You can replace your existing furnace with a whole-house heat pump and utilize your existing ductwork to circulate the conditioned air, but if your house doesn’t have ducts, you don’t need to install them. Ductless mini-split systems consist of wall-mounted units with their own fans mounted in individual rooms and connected the compressor by wires and refrigerant hoses. No ducts required!
About the Experts
- Brooke Greenwood has over two decades of experience in heating and cooling. She is the Director of Product Management at Carrier.
- Kathy Hannun is the co-founder and President at Dandelion Energy, a spinout of Alphabet’s innovation Lab, X, and the nation’s leading home geothermal company.
Sources
- U.S. Department of Energy: Heat Pump Systems; (2025)
- National Association of Home Builders: Which Heating and Cooling Systems are Most Common for New Homes?; (2021)
More About Heat Pumps
Heat pumps efficiently heat and cool your home by transferring heat, and understanding how they work can help you choose the best one for your home.
