Heat Pump COP Calculator
Calculate a heat pump's coefficient of performance (COP) from its heating capacity and power draw, with optional correction for defrost-cycle losses below 7 °C. Used to compare heat pump models and assess seasonal energy costs.
About this calculator
The Coefficient of Performance (COP) of a heat pump measures how many units of heat energy are delivered per unit of electrical energy consumed: COP = Q_h / W, where Q_h is the heating output in watts and W is the electrical power input in watts. Because heating capacity is often quoted in BTU/h, this calculator converts it using the factor 1 BTU/h = 0.293071 W. When outdoor temperatures drop below 7 °C, frost accumulates on the outdoor coil, triggering periodic defrost cycles that temporarily reduce effective output. The calculator applies a 5 % penalty in this regime: COP = (heatingCapacity × 0.293071) / powerConsumption × 0.95. A higher COP means greater efficiency; air-source heat pumps typically achieve COP values of 2–4 under moderate conditions, far exceeding the COP = 1 of direct electric resistance heating.
How to use
Example: heating capacity = 36,000 BTU/h, power consumption = 3,500 W, outdoor temperature = 2 °C (defrost losses apply). Step 1 — Convert capacity to watts: 36,000 × 0.293071 = 10,550.6 W. Step 2 — Apply defrost correction (outdoor temp < 7 °C): effective output = 10,550.6 × 0.95 = 10,023.0 W. Step 3 — Calculate COP: 10,023.0 / 3,500 ≈ 2.86. This means for every 1 kWh of electricity consumed, the heat pump delivers 2.86 kWh of heat — saving about 65 % compared to a direct electric heater. Enter your unit's rated values to find your system's COP.
Frequently asked questions
What is a good COP for an air-source heat pump in cold weather?
A COP above 2.0 is generally considered acceptable for an air-source heat pump operating in cold conditions (below 5 °C). Modern inverter-driven units from leading manufacturers maintain COP values of 2.5–3.5 at 2 °C outdoor temperature, and values above 4.0 at moderate temperatures around 7–10 °C. Cold-climate heat pumps (CCHP) with enhanced vapor injection compressors can achieve COP > 2.0 even at −15 °C. Below COP = 1.0, supplemental electric resistance heat is more efficient, which is why many systems include a backup element that activates at very low temperatures.
How does outdoor temperature affect heat pump efficiency and heating capacity?
As outdoor temperature drops, the temperature difference between the refrigerant and the outdoor air decreases, making heat extraction progressively harder. Both COP and heating capacity fall together: a unit rated at COP 3.5 and 12 kW at 7 °C might deliver only COP 2.0 and 8 kW at −10 °C. This dual penalty means the system struggles exactly when demand is highest. Manufacturers publish performance curves (H1/H2/H3 test points under AHRI 210/240) to characterize this behavior, and those rated values are what you should enter into this calculator for accurate seasonal estimates.
Why do defrost cycles reduce heat pump efficiency and how significant is the loss?
When outdoor temperatures hover between −5 °C and 7 °C, moisture in the air freezes onto the outdoor coil, gradually blocking airflow and heat transfer. The heat pump periodically reverses its refrigerant flow to melt this ice, consuming electrical energy and temporarily extracting heat from the indoor space instead of delivering it. This calculator applies a 5 % COP reduction to represent this average penalty, which aligns with industry guidance. In practice, the loss depends on humidity and cycling frequency — in very humid near-freezing conditions, defrost can reduce seasonal performance by 10–15 %, while in dry cold climates the effect is minimal.