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Heating

COP vs SCOP for heat pumps

One is a measurement at a single favourable operating point. The other averages a whole heating season.

Published 23 August 2026 · Published by SnapEnergyLab. Methodology and default assumptions are documented separately.

A heat pump beside a house on a damp spring morning with the last patches of melting snow nearby

Quick answer

COP is heat out divided by electricity in, measured in steady state at one pair of temperatures — conventionally +7 °C outdoor air and 35 °C flow. It is a laboratory data point.

SCOP weights performance across a defined distribution of outdoor temperatures for a whole heating season, including part-load behaviour, defrost and auxiliary heat. It is the figure that belongs in a running-cost calculation.

Using COP where SCOP belongs typically overstates savings by 25–35%.

How to read the numbersSourced valueIllustrative modelCalculated result
COP
One operating point
Sourced value
SCOP
A whole season
Sourced value
Typical gap
COP 4.3 → SCOP 3.2
Illustrative model

Two questions, two numbers

COP answers: how efficient is this machine right now, at these conditions? It is essential for engineering comparisons, because it isolates the equipment from the weather and the building.

SCOP answers: how much electricity will this system consume over a heating season? That requires a climate assumption, a load assumption, and accounting for everything the machine does that is not steady-state heating.

Neither is dishonest. The dishonesty is quoting the first while answering the second.

  1. COP = heat delivered (kW) ÷ electrical input (kW) [at one operating point]
  2. SCOP = annual heat delivered (kWh) ÷ annual electricity (kWh)
  4. annual electricity = heat demand ÷ SCOP
  5. annual cost = heat demand ÷ SCOP × price per kWh

Note the units: COP compares powers at an instant, SCOP compares energies over a year. They are not the same kind of quantity.

What SCOP includes that COP does not

Temperature distribution. A season is mostly mild hours and a few severe ones. SCOP weights the bins according to a reference climate — and the standard defines several, so a SCOP quoted for a warm reference climate is not comparable to one quoted for a cold one.

Part-load operation. Inverter units run below full output most of the time, which is generally more efficient. A fixed-speed unit cycles on and off instead, which is less.

Defrost cycles. Energy spent melting frost, plus the heat not delivered during them.

Auxiliary heat. Immersion elements covering the coldest hours run at COP 1 and drag the seasonal figure down disproportionately.

Standby and controls. Crankcase heaters and controls draw power year-round.

Worked example: what the wrong number costs you

  1. Annual heat demand15,000 kWhYour input
  2. Estimate using COP 4.315,000 ÷ 4.3 = 3,488 kWhCalculated result
  3. Cost at 0.30 per kWh1,046Calculated result
  4. Estimate using SCOP 3.215,000 ÷ 3.2 = 4,688 kWhCalculated result
  5. Cost at 0.30 per kWh1,406Calculated result
Annual understatement from using COP360, about 26%

SPF: the number from real installations

Field studies report a seasonal performance factor (SPF) measured in situ rather than a standardised SCOP. SPF includes everything the actual installation does — commissioning errors, oversized flow temperatures, hot-water cycles, the circulation pump — and it is consistently below laboratory SCOP.

Be careful about system boundaries when comparing published SPF figures: SPFH2, SPFH3 and SPFH4 include progressively more of the system, and the numbers fall as the boundary widens. A quoted SPF without its boundary is as ambiguous as a COP without its temperatures.

When in doubt, plan on the low end of what field data shows for your climate and flow temperature. If the economics only work at the datasheet figure, they do not work.

Model the savings with a seasonal figure

Our calculator asks for a seasonal efficiency figure, not a rated COP, and shows both the electricity consumed and the cost so you can see which assumption is doing the work.

Open the heat pump savings calculator

Assumptions and limitations

  • COP and SCOP values used here are illustrative of typical modern air-source equipment, not specifications for any product.
  • SCOP depends on the reference climate used in the test. Compare SCOP figures only when they are stated for the same climate and the same flow temperature.
  • Field-measured SPF is usually lower than laboratory SCOP. Treat the datasheet as an upper bound rather than an expectation.

Sources

  1. EN 14825 — Testing and rating at part load conditions and calculation of seasonal performance — European Committee for Standardization

    Supports: Definition of SCOP, the reference heating seasons and the part-load bins used to compute it.

  2. EN 14511 — Testing and rating of air conditioners and heat pumps — European Committee for Standardization

    Supports: Definition of COP as a steady-state measurement at stated source and sink temperatures.

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