In short
COP on a heat pump is heat out divided by electricity in, measured at one outdoor temperature. A COP of 3 means three units of heat for each unit of electricity. It falls as the weather gets colder, so in Ontario the figure to ask for is the COP at -15°C. Cold-climate models must reach at least 1.75 there.
COP on a heat pump tells you how many units of heat you get for each unit of electricity you pay for, at one stated outdoor temperature. It is the plainest efficiency number a heat pump has. Where it fits among the other ratings is shown in the glossary of heating and cooling terms.
What a COP number means
A COP above 1 is possible because a heat pump moves heat from the outdoor air instead of generating it. Electric baseboards, electric furnaces and the backup strip heater in an air handler are COP 1 by definition: one unit in, one unit out. For gas, the comparable figure is AFUE, where a 96% furnace turns 0.96 of the fuel's energy into heat. Electricity use compared with baseboard heat is simply one divided by the COP.
- COP 1: electric resistance heat, the baseline
- COP 1.75: the minimum at -15°C for a cold-climate listing, about 57% of the electricity baseboards would use
- COP 2: half the electricity of baseboards for the same heat
- COP 3: one-third of the electricity
- COP 4: one-quarter of the electricity
Why the COP at -15°C is the figure that matters in Ontario
COP falls as the outdoor temperature drops, because the compressor has to lift heat across a wider temperature gap and the outdoor coil needs defrosting. The number in a brochure is usually taken at 8.3°C, a mild autumn day. The honest figure for this climate is the COP at -15°C, read together with how much heat the unit still makes at that temperature.
The cold-climate specification requires at least 1.75 at -15°C with the unit at maximum output. You can find the figure for a specific model on its NEEP cold-climate listing or in the manufacturer's extended performance table. If a salesperson quotes a single COP without a temperature, ask which temperature it belongs to.
COP vs HSPF2: one temperature against a whole winter
COP is a snapshot and HSPF2 is the seasonal average. Dividing HSPF2 by 3.412 gives the average COP across a standard heating season. Use COP at specific temperatures to judge cold-day performance and to set the changeover point in a hybrid system, and use HSPF2 to compare annual electricity use.
COP alone does not decide running cost, because gas and electricity are priced differently. In a hybrid system the changeover belongs at the outdoor temperature where the heat pump's COP stops beating the gas furnace on cost per unit of heat, and that depends on your Enbridge Gas and local hydro rates. Worked examples are in our guide to heat pump running costs in Ontario.
What lowers the COP you get at home
The published COP is a lab figure for a correctly installed system. A heat pump that is running poorly can deliver far less, and the first sign is a hydro bill that climbs faster than the weather explains.
- Low refrigerant charge from a leak
- Undersized or leaky ducts that restrict airflow across the indoor coil
- A clogged filter or a dirty outdoor coil
- An outdoor unit buried in snow or boxed in so air cannot move through it
- Thermostat setbacks that call for electric backup heat every morning
- Backup heat staged to come on too early or stuck on
Most of these are found in one maintenance visit. For a new system, a cold-climate heat pump typically costs $6,000–$16,000 installed before rebates, and the cold-weather COP is one of the things that separates the models in that range. ZK Mechanical states the COP at -15°C on each heat pump installation quote; ask for one and bring your last winter's gas and hydro bills.
Questions people ask about COP
What is a good COP for a heat pump in winter?
At -15°C, 1.75 is the entry requirement for a cold-climate listing and stronger models sit above 2. In mild weather around 8°C the same equipment will often run between 3 and 4. Judge a heat pump for an Ontario house by its cold-temperature figure, since every model looks good on a mild day.
Can a heat pump's COP drop below 1?
The compressor running inside its rated temperature range stays above 1. The system as a whole slides toward 1 when electric backup strips do most of the heating, because strip heat is exactly 1. If your bills suggest something worse than baseboards, look for backup heat stuck on, a low refrigerant charge or a unit defrosting constantly.
Is a COP of 3 the same as 300% efficiency?
Yes, a COP of 3 is often written as 300%. It does not break any law of physics, because the extra heat is collected from the outdoor air and moved indoors, not created from electricity. A gas furnace at 96% AFUE and a baseboard heater at 100% cannot exceed 1, since they produce their heat instead of moving it.