How Heat Pumps Work: How a Heat Pump Heats and Cools a Home
One system cools in summer and heats in winter by carrying heat across your walls instead of burning fuel to make it.
One system cools in summer and heats in winter by carrying heat across your walls instead of burning fuel to make it.
The same equipment that cools your house in July can heat it in January. That is the short answer to how a heat pump works: a single system moves heat, and it moves it in one direction in summer and the opposite direction in winter. The U.S. Department of Energy (DOE) explains that heat pumps move heat instead of creating it, and ENERGY STAR describes the cycle behind it in terms of a refrigerant that absorbs and releases heat as its pressure changes. This guide walks through summer, winter, the savings the DOE reports, cold weather limits, and the ratings to check when you compare units.
The Basic Idea: Moving Heat Instead of Making It
A heat pump does not generate warmth the way a furnace or baseboard heater does. According to the DOE Energy Saver article “Pump Up Your Savings,” heat pumps move heat rather than create it. In cold weather they pull heat from the outdoor air into the home, and in warm weather they take heat from inside the home and release it outside. The DOE’s purchasing guidance adds that one system provides both heating and cooling.
The working fluid in the system is a refrigerant. ENERGY STAR explains that the refrigerant changes between liquid and gas depending on its pressure. At low pressure it absorbs heat and evaporates. At high pressure it releases heat and condenses.
How a Heat Pump Cools in Summer
In summer, ENERGY STAR notes, a heat pump works like an ordinary air conditioner. It takes heat out of the indoor air and sends it outside. The refrigerant absorbs heat from your rooms and carries it out of the house.
How a Heat Pump Heats in Winter
In winter, according to ENERGY STAR, the same cycle runs in reverse. ENERGY STAR points out that cold outdoor air still contains heat. The refrigerant absorbs that heat outside, is then pressurized so its temperature rises, and releases the heat inside the house.
Quick Self-Check
Look at how your home is heated right now. Is it a gas furnace, an electric furnace, electric baseboard heaters, or something else? Your answer matters, because the savings the DOE describes are measured against electric furnaces and baseboard heaters, and your starting point decides how relevant those figures are to you.
What the DOE Reports About Savings
The DOE Energy Saver article says modern heat pumps can cut electricity use by about 50% compared with electric furnaces and baseboard heaters. A separate DOE page on residential improvements gives a different figure for the same comparison, about 65% less electricity for heating. Because the two DOE pages do not agree, it is more honest to say the savings are substantial but not exactly known for your home. The same residential page also says heating typically accounts for about 30% of a home’s energy bill, which is why the choice of equipment matters.
What Happens in Cold Weather
Cold weather is where heat pumps get the most scrutiny. DOE and Oak Ridge National Laboratory material says that the capacity and efficiency of conventional air source heat pumps drop significantly when the outdoor temperature falls. Models designed for cold climates exist to reduce that problem. The DOE’s purchasing guidance says cold climates call for specially designed heat pumps that can operate at lower ambient temperatures before switching over to electric resistance heating.
ENERGY STAR’s cold climate certification requires third-party verified performance at low temperatures, with testing down to 5 degrees Fahrenheit. According to ENERGY STAR, units keep operating below 5 degrees Fahrenheit, but they perform better with a backup heat source at the lowest temperatures. Ask a manufacturer for performance data that matches your local winters. The National Renewable Energy Laboratory adds that more research on cold climate performance is needed and that the biggest savings come from pairing the heat pump with a well-built building envelope.
What to Look for When Comparing Units
Efficiency is rated in SEER2 for cooling and HSPF2 for heating, both expressed in Btu per watt-hour, according to the DOE. ENERGY STAR sets minimums for residential models. A split system must reach an HSPF2 of 7.8, a SEER2 of 15.2, and an EER2 of 11.0, while a single-package system must reach an HSPF2 of 7.2, a SEER2 of 15.2, and an EER2 of 10.0. Confirm the current criteria before you buy.
Cold climate certification is stricter. It requires a SEER2 of at least 15.2 for every type, and an HSPF2 of at least 8.5 for ductless split systems or 8.1 for ducted split and single-package systems. They must also deliver a coefficient of performance of at least 1.75 at 5 degrees Fahrenheit. The ratings changed from the older HSPF and SEER labels to HSPF2 and SEER2 in January 2023, so read the label carefully when comparing.
Heat pumps also sit inside a larger energy picture. For background on how electricity reaches homes, see our article on the smart grid, and for developments in energy storage, see our piece on next-generation battery technology.
What This Means for You
A heat pump is one system doing two jobs by moving heat: out of the house in summer and into it in winter. If you now heat with electric furnaces or baseboard heaters, the DOE figures suggest meaningful savings, with one DOE page citing about 50% and another about 65%. If you live somewhere very cold, look for cold climate certification and ask what backup heat the unit uses. The percentages here are general guidance, not a forecast of your own results.
Frequently Asked Questions
Does a heat pump create heat?
No. The DOE says heat pumps move heat rather than create it. In winter they bring heat from the outdoor air inside, and in summer they take heat from inside and release it outside.
Can a heat pump work when the air outside is cold?
ENERGY STAR says cold outdoor air still contains heat that the refrigerant can absorb. Cold climate certified units are tested down to 5 degrees Fahrenheit and keep operating below that, though they perform better with a backup heat source at the lowest temperatures.
How much electricity can a heat pump save?
The DOE Energy Saver article says about 50% less than electric furnaces and baseboard heaters, while another DOE page says about 65% less electricity for heating. Your result depends on your home, climate, and electricity prices.
What do SEER2 and HSPF2 mean?
According to the DOE, SEER2 rates cooling efficiency and HSPF2 rates heating efficiency, both in Btu per watt-hour. They replaced the older SEER and HSPF labels in January 2023.
This content is for informational purposes only and does not constitute personalized financial advice. Terms and conditions change, so confirm the details with the official provider before making a decision.
Last reviewed: 2026-10-18
Sources consulted:
https://www.energystar.gov/products/ask-the-experts/how-does-heat-pump-work
https://www.energy.gov/cmei/femp/purchasing-energy-efficient-residential-air-source-heat-pumps
https://www.energystar.gov/products/air_source_heat_pumps/key-product-criteria
https://www.energystar.gov/products/air_source_heat_pumps
https://www.energy.gov/articles/pump-your-savings-heat-pumps
https://www.energy.gov/node/4839782
https://www.energy.gov/node/1742956
https://arctic.gov/uploads/assets/aserc-marsik.pdf
