Heat Pump COP from Capacity & Power

A heat pump's efficiency is not one number — it changes with the outdoor temperature. Enter the heat output (BTU/h) and electrical input (watts) from the unit's performance data at a temperature and get the COP at that point, the coefficient of performance that says how many units of heat you get per unit of electricity.

Estimate: results come from the values you enter and standard reference constants. Get real written quotes and check your utility bill before you decide.
Refrigerant: Handling refrigerant requires EPA Section 608 certification — DIY charging is illegal and dangerous. This tool does not cover refrigerant work.

Calculator

BTU/h
Capacity at the outdoor temp of interest
W
Compressor + fan power draw
Coefficient of performance3.00
Heat output36,000 BTU/h
Electrical input3,517 W (3.52 kW)

Delivering 36,000 BTU/h for 3,517 W is a COP of 3.00 at that outdoor temperature (COP = BTU/h ÷ (W × 3.412)).

The coefficient of performance (COP) is the cleanest way to describe a heat pump: it is simply the heat delivered divided by the electricity consumed, both in the same energy units. A COP of 3 means three units of heat into the house for every unit of electricity drawn — roughly 300% "efficient" compared with the 100% ceiling of resistance heat. Unlike the seasonal HSPF2 rating, COP is a point value: manufacturers publish it (or the capacity and power it is derived from) at several outdoor temperatures, because both the heat a unit can make and the power it draws shift as it gets colder. This tool turns a capacity and a power draw into the COP at that operating point.

Formula

Convert the electrical input to the same units as the heat output, then divide:

COP = heat output (BTU/h) ÷ (power (W) × 3.412)

The factor 3.412 converts watts to BTU/h (1 W = 3.412 BTU/h), so both quantities are in BTU/h and the COP is a pure, unitless ratio. Higher is better: more heat delivered for the same power means a lower running cost.

Worked example

Suppose the performance table lists 36,000 BTU/h of heat output for a 3,517 W draw at a given outdoor temperature:

COP = 36,000 ÷ (3,517 × 3.412) = 36,000 ÷ 12,000 = 3.0

So the unit is running at COP 3.0 at that temperature — it delivers three times as much heat as the electricity it consumes. Read the capacity and power at a colder temperature and the COP will be lower; do it at a mild temperature and it will be higher. Collect a few points this way and you can see the whole efficiency curve, then feed the relevant COP into the balance-point and running-cost tools.

Where to find the numbers

Manufacturers usually publish "expanded performance data" or a submittal sheet with capacity (BTU/h) and power (kW or W) at outdoor temperatures like 47°F, 35°F, 17°F and 5°F. Enter the pair for the temperature you care about — watts, not kilowatts (multiply kW by 1,000). If the sheet lists total power in kW, a 3.517 kW draw is 3,517 W. The result is the steady-state COP and does not include defrost penalties or cycling losses, so a real seasonal average will be a bit lower than the best point values.

COP and HSPF2 measure related things: COP is an instantaneous ratio, while HSPF2 is a seasonal figure in BTU per watt-hour. A rough conversion is HSPF2 ≈ COP × 3.412; the COP ↔ HSPF2 converter makes that explicit. Use COP for point-by-point comparisons and HSPF2 for whole-season estimates.

Frequently asked questions

What is a good COP for a heat pump?
At mild temperatures around 47°F many heat pumps hit COP 3.5–4.5; at 17°F a cold-climate unit might still hold COP 2–2.5, while a standard unit drops further. Anything above 1 beats electric resistance heat, but the higher the COP the cheaper it is to run.
Why does COP fall as it gets colder?
A heat pump moves heat from outdoor air into your home. The colder it is outside, the less heat is available to move and the harder the compressor works, so it delivers less heat for more electricity — the COP drops. That is why cold-climate units and dual-fuel backups exist.
How is COP different from HSPF2?
COP is a point value — heat out divided by electricity in at one operating condition. HSPF2 is a seasonal rating in BTU per watt-hour that blends many conditions. Roughly, HSPF2 ≈ COP × 3.412, but use COP for a specific temperature and HSPF2 for a whole heating season.
Do I enter watts or kilowatts?
Watts. If the performance sheet gives power in kilowatts, multiply by 1,000 first — 3.517 kW is 3,517 W. Mixing up the two will make the COP off by a factor of a thousand.
Does this COP include the outdoor and indoor fans?
It includes whatever power figure you enter. Manufacturer total-system power usually covers the compressor and both fans; if you only enter compressor watts you will get an optimistic COP. Use the total input power for a realistic number.

Related calculators

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