SEER and SCOP are seasonal efficiency scores for an air conditioner that also heats. SEER covers cooling across a cooling season. SCOP covers heating across a heating season. A higher score means less electricity for the same heating or cooling under the test method. The score on the label is a comparison tool for matched equipment, not a promise for a west-facing flat with a dirty filter. Fix capacity and outdoor position on survey, then use the scores to choose between honest options.
What SEER is adding up
SEER is the seasonal energy efficiency ratio for cooling. It rolls a spread of outdoor temperatures, part-load running and standby into one figure, which is why it replaced a single hot-day test on current labels. Air-to-air heat pumps, in the Energy Saving Trust sense, earn that score because they move heat rather than warming a room with a resistance element. A brochure line that quotes only the best laboratory point is a different number.
What SCOP is adding up
SCOP is the seasonal coefficient of performance for heating, built the same way across a heating season. Cold weather is part of the idea of the test. A damp February behind a north wall can still be harsher than the seasonal average, so ask how that outdoor model behaves in heating, including ordinary defrost pauses. A strong SCOP matters in a house that will lean on the split in spring and autumn.
Same range, different capacity
Ask for SEER and SCOP on the exact indoor and outdoor pair at the capacity you are buying. A 2.5 kW combination and a 5 kW combination from the same range do not share one badge. Adding room labels on a multi-split overstates what the system will do. Use the certified combination for that outdoor unit and those indoors.
- Compare the same capacity and the same climate column on the label.
- The test assumes a clean filter and a free path of air at the outdoor unit.
- An energy class with no model codes is not a comparison you can check.
Two quotes, one room
Manufacturers publish SEER and SCOP for a matched combination. Change the indoor, the outdoor, or the pipe-length class and the certified figure can move. Inverter control, which most current UK splits use, already sits inside those seasonal tests because the compressor spends much of the year below full speed. A fixed-speed unit can look acceptable on one afternoon and poor across a season. That is a reason to read SEER, and a reason to keep the room-load calculation in view.
Lantern roofs and dirty filters
SEER does not remove heat from a lantern roof that was never in the test. SCOP does not heat a bedroom if the outdoor unit is starved of air in a lightwell. A clogged filter, a refrigerant leak left for an F-gas engineer, a machine that is far too large, and a July setpoint of 18C all pull the bill away from the sticker. A small SEER gap is often smaller than the effect of setpoint, open windows and a blocked outdoor coil. The company that works on the refrigerant circuit still needs the right F-gas company certification and certified people, whichever label prints the higher number. GOV.UK publishes that certification guidance.
Hours, tariffs and the models on the sheet
Hours of use and the tariff do the rest. A strong SEER matters in a top-floor flat that runs through every hot week. Many UK homes care about both scores, which is why the survey specifies a reverse-cycle pair rather than cooling alone. Ask for indoor model, outdoor model, cooling capacity, heating capacity at a stated outdoor temperature, SEER, SCOP and the energy class. Then compare pipe route, condensate method and who registers the warranty. Those site items never appear inside SEER, and they often outweigh a small gap between two close scores. If one quote looks efficient and cheap, check that the outdoor unit is the one on the data sheet. Outdoor siting still needs a look at the Planning Portal page on air source heat pump permission where the unit is heating plant.
Frequently asked questions
Is a higher SEER always cheaper to run?
Only when the unit is the right size, the filter stays clean and the hours of use are similar. A small SEER gap is often smaller than the effect of setpoint, open windows and a blocked outdoor coil.
Core buying guides
Start with these high-intent guides, then dig into the rest of the library.
Related guides
Sources and further reading
How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.