Quick answer
The coefficient of performance (COP) is the ratio of useful heat a heat pump delivers to the energy it uses, both in the same units, at one set of operating conditions; a COP of 3 means three units of heat for every unit of electricity.
Electric resistance heat has a COP of 1. Heat pumps beat it because they move heat rather than make it, and their COP falls as the outdoor air gets colder.
Quick facts
The key facts about Coefficient of Performance (COP), with sources:
- Formula
- COP = heat delivered ÷ energy input (same units, so no unit)
- Electric resistance heat
- COP 1.0 by definition
- Link to HSPF2
- Seasonal COP ≈ HSPF2 ÷ 3.412 3
- ENERGY STAR cold-climate test
- COP 1.75 or higher at 5°F (Appendix M1 H42 test) 1
- ENERGY STAR geothermal, closed loop water-to-air
- COP 3.6 or higher 2
- Used for
- Heat pumps, geothermal systems, chillers, refrigeration
Key takeaways
- COP is heat out divided by energy in. Higher is better; 1.0 is the score for plain electric heat.
- It is a snapshot at one temperature. HSPF2 is the seasonal average, and HSPF2 ÷ 3.412 gives the average COP.
- An air-source heat pump’s COP drops as it gets colder outside. ENERGY STAR cold-climate units must hold 1.75 at 5°F 1.
- Geothermal heat pumps have higher, steadier COPs because the ground stays mild 2.
- At a COP above 1, a heat pump beats resistance heat on energy, but fuel prices decide whether it beats gas.
What COP measures
COP compares two amounts of energy in the same units. Heat delivered in kilowatts, divided by electric power used in kilowatts. Because the units cancel, COP is a plain number.
A space heater turns every watt into a watt of heat, so its COP is 1.
A heat pump uses electricity to run a compressor that pulls heat from outdoor air, the ground or water, and pumps it inside.
At 47°F outside, many air-source heat pumps deliver three or more watts of heat per watt used.
One kilowatt-hour equals 3,412 BTU 3. That is why you can turn the seasonal rating HSPF2 into an average COP by dividing by 3.412. ENERGY STAR uses COP directly for its cold-climate test, which requires a COP of at least 1.75 at 5°F 1.
Why a heat pump can deliver more heat than the power it uses
- Cold refrigerant in the outdoor coil absorbs heat from the air → it evaporates
- Compressor uses electricity to squeeze the vapor → it gets hot
- Hot vapor gives off heat in the indoor coil → your home warms
- Expansion valve drops the pressure → refrigerant goes back outside to pick up more heat
- Heat delivered = heat picked up outside + compressor work → COP above 1
Why COP changes with the weather
The colder it is outside, the further the heat pump must lift heat to reach indoor temperature. The compressor works harder for each unit of heat, so COP falls. Physics sets a ceiling: the bigger the temperature gap, the lower the best possible COP.
That is why spec sheets list COP at several temperatures, such as 47°F, 17°F and 5°F. A unit may show a COP near 4 at 47°F and under 2 at 5°F. Defrost cycles also cut real-world COP in damp cold weather, since the unit spends some time melting ice off its outdoor coil.
Ground-source systems avoid most of this. Soil a few feet down stays far milder than winter air, so the lift is smaller and COP stays higher and steadier. ENERGY STAR requires a COP of at least 3.6 for closed-loop water-to-air geothermal heat pumps 2.
COP benchmarks you will see
| Benchmark | COP | Source |
|---|---|---|
| Electric resistance heat (baseboard, strips) | 1.0 | By definition |
| ENERGY STAR cold-climate air-source, at 5°F | 1.75 or more | ENERGY STAR 1 |
| Federal floor split heat pump, seasonal (7.5 HSPF2 ÷ 3.412) | about 2.2 | 10 CFR 430.32 6 |
| ENERGY STAR split heat pump, seasonal (7.8 HSPF2 ÷ 3.412) | about 2.3 | ENERGY STAR 1 |
| ENERGY STAR geothermal, closed-loop water-to-air | 3.6 or more | ENERGY STAR 2 |
| ENERGY STAR geothermal, open-loop water-to-air | 4.1 or more | ENERGY STAR 2 |
COP and the four label ratings
| Rating | Relation to COP | What it adds | What it hides |
|---|---|---|---|
| COP (this page) | The base ratio, at one condition | Shows cold-weather behavior point by point | No season, no weighting |
| HSPF2 | Seasonal heating COP × 3.412 | One number for a moderate winter | Hours below 17°F |
| EER2 | Cooling COP × 3.412, at 95°F | Peak summer efficiency | Mild days, heating |
| SEER2 | Seasonal cooling COP × 3.412 | One number for a summer | Peak heat, heating |
| AFUE | Not a COP; fuel-to-heat percent, max 100% | Furnace and boiler efficiency | Cannot exceed 1 as a ratio |
Example: cost per million BTU at different COPs
One million BTU is 293 kWh of heat (1,000,000 ÷ 3,412) 3. Electricity: US residential average 18.31¢ per kWh, July 2026 4. Cost per million BTU = 293 ÷ COP × price.
| COP | kWh used per million BTU | Energy cost per million BTU |
|---|---|---|
| 1.0 (resistance) | 293 | about $53.66 |
| 1.75 (cold-climate floor at 5°F) | 167 | about $30.66 |
| 2.5 | 117 | about $21.46 |
| 3.5 | 84 | about $15.33 |
Compare with gas: at $13.96 per thousand cubic feet in January 2026 5, and 1,036 BTU per cubic foot 3, one million BTU of gas costs about $13.47.
At 95% AFUE, delivered heat costs about $14.18 per million BTU. With these national averages, gas wins until the heat pump’s COP passes about 3.8. Your local prices change the answer; see our electric vs gas price ratio research.
Where you will find COP
- On spec sheets, in heating performance tables at 47°F, 17°F and 5°F.
- On the NEEP cold-climate product list, which reports COP at low temperatures 7.
- On geothermal AHRI ratings and data sheets, as COP at standard water temperatures 8.
- In rebate rules for cold-climate heat pumps, which often cite COP at 5°F.
- Not on the yellow EnergyGuide label for air-source units, which uses HSPF2.
Why COP is useful
Good for
- Comparing cold-weather performance where HSPF2 is silent.
- Working out cost per unit of heat against gas, oil or propane.
- Comparing air-source, ground-source and resistance heat on one scale.
- Finding the temperature where a dual-fuel system should switch to gas.
Watch out for
- A single point says nothing about the season.
- Makers may quote the best point. Check the temperature beside the number.
- Lab COP may leave out defrost and backup strip heat.
- Does not include duct losses or a poor install.
Limits of a COP figure
COP is measured under steady lab conditions with correct charge and airflow. In real homes, installation faults matter. NIST found low refrigerant charge, low indoor airflow and duct problems among the faults that most raise heat pump energy use 9.
COP also varies with capacity. A variable-speed heat pump running slowly on a mild day can post a higher COP than at full speed. Always check whether a COP was measured at minimum, rated or maximum capacity.
Sources: [9]
Cost drivers that move COP
Higher COP at low temperatures usually comes from a variable-speed compressor, larger coils and enhanced vapor injection. Ground loops raise COP further but add drilling or trenching.
Prices are not listed here. HyreHVAC publishes cost figures only with enough dated quotes. Use the heat pump savings calculator to test your own COP and fuel prices.
How to use COP when choosing a heat pump
- Find your winter design temperature from your contractor’s load calculation.
- Ask for the spec sheet’s COP and capacity at 17°F and 5°F for the exact pair.
- Check whether the COP is at maximum or rated capacity.
- Compare cost per million BTU at your power and gas prices, as in the example.
- If you keep a furnace, use the COP curve to set a switchover temperature.
Install and refrigerant work are for licensed, EPA Section 608 certified technicians.
Keeping COP high in daily use
- Keep filters clean; low airflow lowers COP 10.
- Clear snow from around the outdoor unit and keep its drain path open.
- Avoid deep setbacks that bring on backup strips, which run at COP 1.
- Ask for an annual check of charge and airflow 10.
Sources: [10]
Signs your real COP is low
- Backup or "aux" heat runs often above freezing.
- The outdoor coil stays iced and defrost seems to fail.
- Winter bills look like electric baseboard bills.
- Air from vents feels lukewarm for long periods.
- Call a licensed technician; do not adjust refrigerant or open the electrical panel.
Rules and standards that use COP
Federal efficiency standards for central heat pumps use HSPF2, not COP 6. ENERGY STAR uses COP in two places: the cold-climate tier for air-source heat pumps (1.75 or more at 5°F, measured with the Appendix M1 H42 test) 1, and geothermal criteria by loop type, effective since 1 January 2012 2.
The NEEP cold-climate specification, version 4.0 since 1 January 2023, also reports low-temperature COPs 7. Many state rebate programs reference it.
COP misconceptions
- Myth A COP above 1 breaks the laws of physics.
- Reality No. The heat pump moves heat that already exists; it does not create it.
- Myth A heat pump with a high COP is always cheaper than gas.
- Reality Only if the price ratio is right. The example shows the break-even.
- Myth COP and HSPF2 are different measures.
- Reality HSPF2 is a seasonal COP in different units.
- Myth COP drops to 1 at freezing.
- Reality Modern units stay well above 1 at 32°F; cold-climate units hold 1.75 at 5°F.
Climate sets your real COP
In mild-winter states such as Florida, Georgia or Texas, most heating hours sit well above 32°F, so a heat pump runs at high COP. In Ohio or inland Washington, more hours fall below freezing, so seasonal COP is lower. Use heating degree days to see how cold your season runs.
When COP should drive your decision
Look at COP when you live where winters drop below 17°F, when you compare against gas or propane, or when you set up a dual-fuel system. A useful test: if your heat pump’s COP at your typical January temperature beats your local price ratio of electricity to gas, run the heat pump.
Next step: compare running cost with the heat pump vs furnace tool and read our cold-climate performance research.
Questions about Coefficient of Performance (COP)
What is a good COP for a heat pump?
A good heating COP is 3 or more at 47°F and 1.75 or more at 5°F, the ENERGY STAR cold-climate floor.
Geothermal systems should reach 3.6 or more under ENERGY STAR closed-loop criteria. Seasonal COP for a new split heat pump is about 2.2 at the federal floor. Always check what temperature a COP was measured at.
How is COP calculated?
Divide heat delivered by energy used, in the same units. A heat pump that delivers 9 kW of heat while drawing 3 kW of power has a COP of 3. To get COP from HSPF2, divide by 3.412. To get it from EER2 for cooling, also divide by 3.412.
What is the difference between COP and HSPF2?
COP is one moment at one temperature. HSPF2 is a whole heating season averaged under the federal test, expressed in BTU per watt-hour. HSPF2 ÷ 3.412 equals the seasonal average COP. Use HSPF2 to compare models and COP at 5°F to judge cold-weather behavior.
Why does COP drop in cold weather?
Because the heat pump must lift heat across a bigger temperature gap. The compressor does more work for each unit of heat delivered. Defrost cycles in damp cold weather cut COP further. Ground-source systems lose less because soil stays mild in winter.
Can a heat pump have a COP below 1?
Not by itself while running normally, but the system can if backup electric strips run, since strips have a COP of 1. Long defrost cycles and faults can pull real-world efficiency down. A system that often runs near COP 1 should be checked by a licensed technician.
What COP do I need to beat gas heat?
It depends on your prices. Using July 2026 US average electricity at 18.31 cents per kWh and January 2026 gas at $13.96 per thousand cubic feet, a heat pump needs a COP of about 3.8 to match a 95% furnace. Cheaper power or pricier gas lowers that bar. Use your own bills.
Does COP apply to air conditioners?
Yes, as cooling COP: heat removed divided by energy used. US ratings express it as EER2 or SEER2 in BTU per watt-hour instead. Divide either by 3.412 to get the cooling COP. Commercial chillers often list COP directly.
What COP does ENERGY STAR require at 5°F?
ENERGY STAR cold-climate air-source heat pumps must have a COP of at least 1.75 at 5°F, measured using the Appendix M1 H42 test. They must also keep at least 70% of their 47°F heating capacity at 5°F and pass a controls verification procedure.
Sources
- ENERGY STAR, Air-Source Heat Pumps key product criteria (incl. cold-climate COP at 5°F), retrieved .
- ENERGY STAR, Geothermal Heat Pumps key product criteria (effective 1 January 2012), retrieved .
- U.S. EIA, Energy Explained: British thermal units (Btu), retrieved .
- U.S. EIA, Electric Power Monthly, Table 5.6.A Average price of electricity by state, July 2026 and 2025, retrieved .
- U.S. EIA, U.S. Price of Natural Gas Delivered to Residential Consumers (monthly), retrieved .
- eCFR, 10 CFR 430.32 Energy and water conservation standards (current text), retrieved .
- NEEP, Cold Climate Air Source Heat Pump Specification and Product List (Version 4.0), retrieved .
- AHRI Directory of Certified Product Performance, retrieved .
- NIST Technical Note 1848, Sensitivity Analysis of Installation Faults on Heat Pump Performance (2014), retrieved .
- ENERGY STAR, Maintenance Checklist for heating and cooling, 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: COP thresholds read from ENERGY STAR air-source and geothermal criteria pages; HSPF2 floors from 10 CFR 430.32; BTU conversion and prices from EIA. Break-even arithmetic shown in full; prices are national averages for the stated months.
Suggest a correction. We fix errors and say what changed.