Heat pump efficiency: what the ratings mean and what changes them
A heat pump can move more heat than the electricity it uses, which is why it can beat a furnace on paper. Whether it does in your house depends on a few things the spec sheet cannot see.
How can a heat pump be more than 100% efficient?
A heat pump does not make heat by burning something or by running current through a coil. It moves heat that already exists, from one place to another, and the electricity pays for the moving. That is why its efficiency can come out above 100% when measured as heat delivered per unit of electricity used.
A resistance heater cannot do this. Every unit of electricity becomes at most one unit of heat. A heat pump in mild weather can deliver several units of heat for each unit it consumes. That gap is the whole case for the technology.
The catch is that the ratio shrinks as the outdoor air gets colder. There is less heat to pull out of the air, so the machine works harder for each unit it delivers.
Which ratings describe a heat pump?
A heat pump carries more than one number because it does two jobs. Each rating answers a different question.
| Rating | What it describes | Where it applies |
|---|---|---|
| SEER2 | Seasonal cooling efficiency | Cooling mode |
| HSPF2 | Seasonal heating efficiency | Heating mode |
| EER2 | Cooling efficiency at one fixed hot condition | Cooling, peak heat |
| COP | Heat delivered per unit of electricity at one specific temperature | Heating, any single condition |
The first two are seasonal averages from a laboratory test run under fixed conditions. COP is a snapshot at one outdoor temperature. A unit can have a strong seasonal number and a weak COP on the coldest morning of the year.
If you live somewhere cold, the heating numbers matter more than SEER2. Many buyers read only the cooling rating because it is the famous one. That is a mistake in a heating-dominated climate.
What changes real-world efficiency
The rating is a comparison tool between machines. It is not a forecast of your result. Several things decide how close you get.
- Outdoor temperature. Heating output and efficiency both drop as it gets colder. Cold-climate models are built to hold up better at low temperatures, but none escape the trend.
- Ductwork. Leaky or undersized ducts waste a share of the heat before it reaches a room. The best unit in the world cannot fix that.
- Sizing. An oversized unit cycles on and off. That hurts comfort and efficiency at the same time.
- Airflow. A clogged filter or a dirty indoor coil cuts the heat the system can move.
- Defrost cycles. In cold, damp weather the outdoor coil frosts over and the system has to melt it. That uses energy and produces no useful heat for a few minutes.
- Backup heat. When the heat pump cannot keep up, electric resistance strips take over. They are far less efficient, so how often they run matters a lot.
Variable speed is the feature worth understanding
A single-stage heat pump is either on or off. A variable-speed one adjusts its output to the load. It runs longer at a lower speed, which is usually quieter, steadier in temperature and more efficient. Most of the highest ratings in any lineup come from variable-speed machines.
It is not magic. If the ducts are poor or the unit is the wrong size, variable speed will not rescue it. But when everything else is right, it is the upgrade that shows up in both comfort and the efficiency numbers.
Is a higher rating worth chasing?
Sometimes, and often less than the brochure suggests. A mild climate with moderate heating needs gets little from the top tier, because the machine rarely works hard enough for the gap to matter. A cold climate with long heating seasons gets far more.
Look at the heating rating first, then at how the model behaves at low temperatures, then at the rating you were about to compare. Ask your installer for the low-temperature performance of the specific model, not just the headline number. And do not pay for efficiency in the cooling rating if you mostly need heat.
This article does not quote prices, rebates or tax credits. Those change constantly and differ by state and utility. Your installer and your state energy office have the current figures that apply to you.
Frequently asked questions
What is a good efficiency rating for a heat pump?
There is no single good number, because the federal minimum is raised periodically and the right target depends on your climate. Compare models by their heating rating (HSPF2) if you live somewhere cold, and by their cooling rating (SEER2) if cooling dominates. Check both against the current minimum for your region.
Why does my heat pump seem less efficient in winter?
Because there is less heat in cold outdoor air to move indoors, so the machine does more work for each unit of heat it delivers. Defrost cycles and backup resistance heat also lower the average. This is normal, and cold-climate models are designed to lose less.
Is COP the same as HSPF2?
No. COP is the heat delivered per unit of electricity at one specific outdoor temperature. HSPF2 is a seasonal average across a range of conditions, expressed in different units. They describe the same idea at different scales.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- ENERGY STAR. Energy Savings at Home: Heating & Cooling
- US EPA. Section 608 of the Clean Air Act