A heat pump's efficiency (COP) and heating output both drop as the outdoor temperature falls. A standard model can lose 40 to 50 percent of its rated capacity by 5°F, while a cold-climate or hyper-heat unit is built to hold roughly 70 to 100 percent at 5°F and keep running below zero, at a lower but still useful COP.
The catch is that the number on the brochure is measured at 47°F, a mild day. What decides whether your house stays warm is how much heat the unit still makes on the coldest normal night, and how efficiently it makes it. Those two things, capacity and COP, both fall with temperature, and they fall much faster on a standard unit than on a cold-climate one.
How COP and capacity change with temperature
The table below shows typical, defensible ranges, not exact specs. Every model is different, so treat these as a way to read a spec sheet, not as a rating for any one unit. Verify the real numbers for a specific model against its AHRI certificate, the manufacturer submittal sheet, or the NEEP cold-climate database before you rely on them.
| Outdoor temp | Standard heat pump COP | Standard capacity retained | Cold-climate / hyper-heat COP | Cold-climate capacity retained |
|---|
| 47°F | 3.0 to 3.8 | ~100% (rated point) | 3.3 to 4.2 | ~100% |
| 35°F | 2.5 to 3.2 | 85 to 95% | 2.8 to 3.6 | 95 to 100% |
| 17°F | 1.8 to 2.4 | 60 to 70% | 2.1 to 2.9 | 85 to 100% |
| 5°F | 1.4 to 2.0 | 45 to 60% | 1.8 to 2.5 | 70 to 100% |
| -5°F | often on backup heat | 30 to 45% (if still running) | 1.5 to 2.1 | 55 to 85% |
Two things stand out. A standard unit and a cold-climate unit can look almost identical at 47°F, where both are rated. The gap opens up in the cold: by 5°F the standard unit may be down near half its output while the cold-climate unit is still close to full.
What COP actually measures
COP, or coefficient of performance, is heat delivered divided by electricity consumed, at a single set of conditions. A COP of 3.0 means the unit moves three units of heat for every one unit of electricity it draws. Electric resistance backup heat has a COP of about 1.0, so even a heat pump running at COP 1.8 in deep cold is still cheaper to run than the strips.
COP is a snapshot at one temperature. HSPF and the newer HSPF2 roll many hours together into a season-long average, which is useful for comparison but hides how the unit behaves on the worst night. For cold-climate planning, the point-in-time COP and capacity at your design temperature matter more than the seasonal average.
Why capacity derates in the cold
A heat pump gathers heat from outdoor air. The colder that air, the less heat there is to gather, so output falls even as the house needs more. This is capacity derating, and it is physics, not a defect. At the same time the unit periodically stops heating to melt frost off the outdoor coil, which trims delivered output further in cold, damp weather.
The result is a squeeze. Household heat demand rises as it gets colder, while a standard heat pump's supply falls. Where those two lines cross is the balance point. Below it, the unit alone cannot keep up and backup heat has to fill the gap.
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Why cold-climate models hold up
Cold-climate and hyper-heat units are engineered to push the balance point much lower. Common design differences include a variable-speed inverter compressor that can overspeed in the cold, enhanced or vapor injection (sometimes called flash injection) that boosts low-temperature output, larger outdoor coils, and smarter defrost logic. Many are rated to keep running and producing usable heat down to -13°F or lower.
That is why a good cold-climate model can still deliver 70 to 100 percent of rated capacity at 5°F. It does so at a lower COP than on a mild day, because moving heat from very cold air always costs more energy, but it keeps the compressor doing the work instead of handing off to resistance heat.
How to use this when comparing quotes
Do not compare heat pumps on the 47°F rating alone, and do not compare on SEER, which is a cooling number. Ask the installer for the model's rated capacity and COP at 17°F and 5°F, then check them against your design temperature, the coldest condition your area normally sees. If the unit's output at that temperature covers your heat loss, you need little or no backup. If it does not, the quote should price and explain the backup heat that makes up the difference.
Frequently Asked Questions
What is a good COP for a heat pump in winter?
At mild temperatures a COP around 3 is typical. In deep cold, anything above 1.5 to 2.0 still beats electric resistance backup, which sits near 1.0. Judge a unit by its COP at your design temperature, not at the 47°F rating point.
Does a heat pump lose all its heat below freezing?
No. Output drops as it gets colder, but a standard unit still delivers meaningful heat at freezing and below, and a cold-climate model can hold most of its capacity well below zero. The question is whether the remaining output covers your home's heat loss on the coldest night.
What does "100% capacity at 5°F" mean on a spec sheet?
It means the unit is engineered to deliver its full rated heating output at 5°F outdoor air, instead of the sharp derating a standard unit shows. Confirm the exact figure on the model's submittal or NEEP listing, since marketing rounds up and ratings are model-specific.
Is a cold-climate heat pump worth it if my winters are mild?
Often not. If your design temperature rarely drops near the range where a standard unit fades, you may be paying for capacity you never use. Match the equipment to your actual climate and heat loss rather than buying the coldest-rated unit by default.
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