Quick answer
A heat pump is an electric system that heats and cools a home by moving heat rather than making it, pulling heat from outdoor air, the ground or water in winter and pushing indoor heat outside in summer.
Because it moves heat instead of burning fuel, it can deliver more heat energy than the electricity it uses. That ratio is its coefficient of performance.
Quick facts
The key facts about Heat Pump, with sources:
- Fuel
- Electricity
- Homes heating mainly with one (2020)
- 16.13 million heat pumps + 1.06 million ductless mini-splits 1
- Heating rating
- HSPF2 (seasonal); COP (at one temperature) 2
- ENERGY STAR cold-climate test
- COP ≥1.75 at 5°F; 5°F capacity ≥70% of 47°F capacity 3
- Refrigerant for new systems
- GWP under 700 (EPA), e.g. R-454B or R-32 4
Key takeaways
- A heat pump is an air conditioner that can also run in reverse to heat.
- It moves heat, so one unit of electricity can deliver more than one unit of heat.
- Output and efficiency drop as it gets colder outside; cold-climate models are tested at 5°F 3.
- About 13% of US homes heat mainly with a heat pump 1.
- Size it for your heating load as well as cooling, and plan the backup heat.
What a heat pump is
Even cold air holds heat. At 20°F, outdoor air still has plenty of heat energy in it compared with absolute zero. A heat pump uses refrigerant to collect some of that heat and carry it indoors. In summer it flips direction and carries indoor heat outside, just like an air conditioner.
Most US heat pumps are air-source: they trade heat with outdoor air. Geothermal (ground-source) heat pumps trade heat with the ground through buried pipes. Water-source units use a well, lake or building water loop.
In 2020, 16.13 million US homes used a heat pump as their main heat, and 1.06 million more used a ductless mini-split heat pump 1.
Heating mode in one line
- Cold liquid refrigerant in the outdoor coil absorbs heat from outdoor air and boils to a gas
- → compressor raises its pressure and temperature
- → reversing valve sends the hot gas to the indoor coil
- → blower moves room air over the hot coil; refrigerant condenses and releases heat
- → expansion device drops the pressure; refrigerant returns outside, cold, to repeat
- Every so often: defrost cycle melts frost off the outdoor coil
How a heat pump works
A heat pump runs the same refrigeration cycle as an AC. The key extra part is a reversing valve. It changes which coil is the cold one and which is the hot one, so the system can heat or cool.
In heating mode the outdoor coil gets colder than the outdoor air, so heat flows into the refrigerant. Below about freezing, moisture in the air turns to frost on that coil. The unit runs short defrost cycles to clear it, which is why you may see steam rising from the outdoor unit in winter.
As outdoor temperatures drop, the heat pump has less heat to collect and must work harder. Capacity and efficiency both fall. That is where backup heat, a cold-climate model or a dual-fuel setup comes in.
Types of heat pumps
| Type | Heat source | Notes |
|---|---|---|
| Ducted air-source (split) | Outdoor air | Most common; replaces AC + furnace or AC alone |
| Ductless mini-split | Outdoor air | Wall or ceiling heads, no ducts |
| Packaged heat pump | Outdoor air | All parts in one outdoor cabinet |
| Cold-climate heat pump | Outdoor air | Holds more capacity below 17°F; ENERGY STAR tests at 5°F 3 |
| Dual fuel | Outdoor air + gas furnace backup | Switches to gas in deep cold |
| Geothermal | Ground loop | Steady source temperature; costly loop |
Worked example: heat out per kWh in
HSPF2 is BTU of heat per watt-hour over a season. Dividing by 3.412 (BTU per watt-hour) turns it into an average COP. Take a home that needs 10,000 kWh of heat delivered in a winter (an assumed load). Ratings from 10 CFR 430.32 and ENERGY STAR 2 3.
| Heat source | Efficiency | Electricity to deliver 10,000 kWh of heat |
|---|---|---|
| Electric resistance (baseboard or strips) | COP 1.0 | 10,000 kWh |
| Heat pump at the federal floor | 7.5 HSPF2 ÷ 3.412 ≈ COP 2.2 | About 4,550 kWh |
| ENERGY STAR split heat pump | 7.8 HSPF2 ≈ COP 2.3 | About 4,370 kWh |
| Cold-climate unit on a 5°F day | COP ≥1.75 (ENERGY STAR test) | About 5,710 kWh if every hour were 5°F |
Even at 5°F, a qualifying cold-climate heat pump uses well under the electricity of resistance heat. Note that HSPF2 is a national test climate; your real seasonal COP depends on your winter. Compare against gas with the heat pump vs furnace tool.
Where heat pump specs appear
- The EnergyGuide label shows SEER2 and HSPF2.
- The AHRI certificate lists capacity at 47°F and 17°F for the matched pair.
- The maker's extended performance table shows capacity and COP at 5°F and colder; ask for it.
- The ENERGY STAR product finder flags cold-climate models.
- The thermostat setup shows a heat pump mode, auxiliary heat and an outdoor lockout setting.
Pros and cons of a heat pump
What it does well
- One system heats and cools.
- Uses much less electricity than resistance heat for the same warmth.
- No combustion indoors, so no carbon monoxide from the heat pump itself.
- Variable-speed models run long and gentle, with even temperatures.
Where it falls short
- Capacity falls in deep cold; non-cold-climate models may lean on backup strips.
- Air from registers feels cooler than furnace air, even when the room is warm.
- Running cost depends on your electric vs gas prices.
- May need an electrical panel upgrade in some homes.
Limits in cold weather
Two numbers matter in cold places: how much heat the unit can still make at your coldest design temperature, and how efficiently.
A standard heat pump may lose a large share of its capacity by 5°F. ENERGY STAR's cold-climate test requires that a qualifying unit still deliver at least 70% of its 47°F capacity at 5°F, with a COP of at least 1.75 3.
The point where the heat pump alone can no longer keep up is the balance point. Below it, backup heat runs. Our cold-climate performance research shows how real models compare.
Cost drivers, lifespan and warranty
What raises the price: capacity, cold-climate or variable-speed design, ducted vs ductless, new ducts, an electrical panel or circuit upgrade, removing an old furnace or oil tank, and permits.
What sets running cost: your local electric and gas prices, your climate, and how often backup heat runs. Our electric vs gas price ratio research shows why the same heat pump saves money in one state and less in another.
Note: the federal 25C tax credit expired on 31 December 2025. Check heat pump rebates for state and utility programs that may still apply. Parts warranties often run longer when the unit is registered.
How a heat pump is installed
- Load calculation for both heating and cooling (Manual J) 6.
- Pick a model whose capacity at your design temperature meets the heating load, not only the cooling load.
- Plan backup heat: electric strips, a furnace (dual fuel) or none for a cold-climate unit sized to the load.
- Permits: mechanical and electrical.
- Set the outdoor unit on a raised stand or pad so defrost water drains and snow does not bury it.
- Evacuate, charge, test both modes and set the thermostat's aux heat lockout.
Keeping a heat pump healthy
- Change or clean the filter; heat pumps are sensitive to low airflow in both modes.
- Keep snow, ice and leaves off and around the outdoor unit; never chip ice off the coil.
- Avoid big thermostat setbacks in winter on older models; recovery may call on strip heat.
- Have a yearly service that checks charge, defrost controls and backup heat.
- Plan seasonal tasks with the maintenance calendar.
Signs a heat pump needs a pro
- Outdoor unit stays coated in thick ice for hours and does not defrost.
- Aux or emergency heat runs constantly on mild days.
- Loud grinding, banging or a burning smell.
- Cold air from vents in heating mode for more than a short defrost.
- Refrigerant leaks; only EPA 608 certified techs can service them 5.
- Repair options are on the heat pump repair page.
Rules that apply to heat pumps
DOE minimums (10 CFR 430.32). Heat pumps made on or after 1 January 2023: split systems 14.3 SEER2 and 7.5 HSPF2; single-package units 13.4 SEER2 and 6.7 HSPF2. Unlike central air conditioners, heat pumps have one national floor, not a regional one 2.
ENERGY STAR. Split systems need at least 7.8 HSPF2, 15.2 SEER2 and 11.0 EER2; single-package units 7.2 HSPF2, 15.2 SEER2 and 10.0 EER2. Cold-climate models add the 5°F tests above 3.
EPA refrigerants. New residential heat pump systems must use a refrigerant under 700 GWP from 1 January 2025; no installation date applies where all parts were made or imported before then 4.
Heat pump vs other heat sources
| System | How it heats | Rating | Also cools |
|---|---|---|---|
| Heat pump | Moves heat | HSPF2 / COP | Yes |
| Gas furnace | Burns fuel | AFUE | No (pairs with AC) |
| Boiler | Heats water | AFUE | No |
| Electric resistance | Heats a coil | COP 1.0 | No |
Common misconceptions
- Myth Heat pumps do not work in the cold.
- Reality Cold-climate models are tested to deliver at 5°F with a COP of at least 1.75 3.
- Myth A heat pump is only for the South.
- Reality Plenty are sold in northern states; the model and sizing matter more than the region.
- Myth Aux heat running means it is broken.
- Reality Aux heat is normal in deep cold or after a large setback; constant use on mild days is not.
- Myth You can still claim the 25C credit for a 2026 install.
- Reality No. The credit expired on 31 December 2025.
Climate decides the right heat pump
Heat pump rules are national, but your winter is not. In Florida, Georgia or Texas, almost any heat pump covers the mild winter, and cooling efficiency drives savings.
In Ohio or eastern Washington, check the capacity at your design temperature and the 5°F rating, or plan dual fuel. Heating degree days show how much heat your home needs each year.
When a heat pump makes sense for you
A heat pump fits well if you need a new AC anyway, heat with electric resistance, propane or oil, or live where winters are mild. It is a closer call if you have cheap natural gas and very cold winters, where dual fuel may be the middle path.
Next step: estimate the savings in the heat pump savings calculator, then see our best heat pumps picks.
Questions about Heat Pump
How does a heat pump work in winter?
It pulls heat out of outdoor air with cold refrigerant, compresses the refrigerant to raise its temperature, and releases that heat indoors. A reversing valve lets the same system cool in summer. Frost on the outdoor coil is cleared by short defrost cycles.
At what temperature does a heat pump stop working?
There is no single cut-off. Capacity and efficiency fall as it gets colder. ENERGY STAR cold-climate models must still deliver at least 70% of their 47°F capacity at 5°F. Many systems switch to backup heat at a set outdoor temperature.
Is a heat pump cheaper to run than a gas furnace?
It depends on your local electric and gas prices and your climate. A heat pump is almost always cheaper than electric resistance, propane or oil heat. Against cheap natural gas in a cold climate, savings can be small or negative.
What is a good HSPF2 rating?
The federal minimum for split heat pumps is 7.5 HSPF2. ENERGY STAR requires at least 7.8 for ducted split systems. Higher numbers mean more heat per kWh. In cold climates, also check the 5°F capacity and COP.
What is aux heat on a heat pump?
Auxiliary heat is backup heat, usually electric resistance strips in the air handler, that runs when the heat pump cannot keep up or during defrost. It is much less efficient, so frequent aux heat on mild days is worth a service call.
Do heat pumps need a backup heat source?
Most installs include one, but a cold-climate heat pump sized to the full heating load may not need it. In very cold areas, backup strips or a gas furnace (dual fuel) protect comfort on the coldest days.
How long does a heat pump last?
Lifespan varies with climate and care. Heat pumps run in both seasons, so they log more hours per year than an AC. Our equipment lifespan research explains what survey data does and does not show.
Is there a tax credit for heat pumps in 2026?
Not under 25C. That federal credit expired on 31 December 2025, so a 2026 install does not qualify. State rebates and utility programs may still apply; check our rebate pages for current status.
Can a heat pump replace my AC and furnace?
Yes. A ducted heat pump can replace a central AC and do some or all of the heating through the existing ducts. Many owners keep the furnace as backup, called dual fuel, especially where winters are long and cold.
Sources
- U.S. EIA, 2020 RECS Table HC6.1, Space heating in U.S. homes, by housing unit type (final data March 2023), retrieved .
- eCFR, 10 CFR 430.32, Energy and water conservation standards (version of 1 September 2026), retrieved .
- ENERGY STAR, Air Source Heat Pumps Key Product Criteria, retrieved .
- U.S. EPA, Technology Transitions HFC Restrictions by Sector, retrieved .
- U.S. EPA, Section 608 Technician Certification, retrieved .
- ACCA, Manual J Residential Load Calculation (8th Edition), retrieved .
Expert review
Written by the HyreHVAC Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Minimums from the eCFR text of 10 CFR 430.32; ENERGY STAR criteria from its key product criteria page; counts from EIA RECS 2020 HC6.1, all read 10 October 2026. The kWh example converts HSPF2 to COP with 3.412 BTU per watt-hour and an assumed heat load.
Suggest a correction. We fix errors and say what changed.