Energy efficiency explained: SCOP, SEER, COP and EER
Efficiency tells you how much heating or cooling a unit delivers for each unit of electricity it draws. Higher is better. You’ll see a few different measures quoted — the two worth comparing between models are SCOP (for heating) and SEER (for cooling).
The four figures, quickly
- COP — heating efficiency at a single test condition
- EER — cooling efficiency at a single test condition
- SCOP — seasonal heating efficiency (a realistic average)
- SEER — seasonal cooling efficiency (a realistic average)
- For all four: a higher number means more output per unit of electricity.
COP and EER — the single-point figures
COP (Coefficient of Performance) measures heating efficiency: a COP of 4 means the unit delivers 4 kW of heat for every 1 kW of electricity it uses — possible because it’s moving heat, not creating it. EER (Energy Efficiency Ratio) is the same idea for cooling. The catch with both is that they’re measured at a single set of test conditions, which won’t match your home all year round.
SCOP and SEER — the figures that matter
The “S” stands for “seasonal”. SCOP and SEER average a unit’s efficiency across a whole heating or cooling season — mild days and hard days together — so they reflect real-world running far better than the single-point numbers. When you’re comparing two units, these are the ones to look at: a higher SCOP means cheaper heating across the year, and a higher SEER means cheaper cooling.
The energy-efficiency label
Air conditioners sold in the UK carry an energy-efficiency label, based on the unit’s seasonal efficiency (SEER for cooling, SCOP for heating), its energy use and its noise. Air conditioners have traditionally used an A+++ to D scale. The simpler A to G scale already used for fridges and washing machines is now being phased in across heating and cooling products, so in 2026 you may see either version — and on the newer A–G scale the top grades are deliberately hard to reach, so a B, C or D can still mark a very efficient unit. The most reliable comparison is the SEER and SCOP figures themselves, not the letter alone. (Labels for the GB market carry a UK flag and a QR code linking to the product’s details.)
Why it matters: efficiency is the single biggest lever on your running costs. A more efficient unit delivers the same comfort for less electricity — and over years of use, the gap really adds up. We put real numbers to this in running costs.