SEER, the seasonal energy efficiency ratio, tells you how much cooling an air conditioner delivers for each unit of electricity across a typical cooling season. A SEER of 8.5 means 8.5 kWh of cooling for every 1 kWh of electricity. On the UK energy label, 8.50 or more is the top A+++ class, and a higher SEER means lower running costs for the same room.
It is the single most useful number on an air conditioner's data sheet, and one of the most misunderstood. Here is how it is measured, what the label bands mean, how it differs from EER and SCOP, and how to turn it into a running cost.
SEER at a glance
| Term | What it measures | Where you see it |
|---|---|---|
| SEER | Seasonal cooling efficiency, averaged over a reference cooling season | Energy label and data sheets for split air conditioners up to 12 kW |
| SCOP | Seasonal heating efficiency, averaged over a reference heating season | Energy label for reversible units |
| EER | Cooling efficiency at one full-load test condition | Data sheets, and the label of portable single and double duct units |
| COP | Heating efficiency at one test condition | Data sheets |
How SEER is worked out
An air conditioner rarely runs flat out. Most of the time it is working at part load on a mild day, and that is where modern inverter units are most efficient. SEER captures that by testing the unit at several outdoor temperatures and weighting the results by how many hours a reference cooling season spends at each one. Manufacturers test to the European standard EN 14825, and Mitsubishi Electric's data sheets, for example, quote their SCOP and SEER figures to BS EN 14825.
The UK labelling rules for air conditioners, retained from EU Regulation 626/2011, define one cooling season and three heating seasons, average, colder and warmer. Every label must show cooling and the average heating season, while colder and warmer figures are optional.
The energy label bands
| Class | SEER (cooling) | SCOP (heating, average season) |
|---|---|---|
| A+++ | 8.50 or more | 5.10 or more |
| A++ | 6.10 to under 8.50 | 4.60 to under 5.10 |
| A+ | 5.60 to under 6.10 | 4.00 to under 4.60 |
| A | 5.10 to under 5.60 | 3.40 to under 4.00 |
| B | 4.60 to under 5.10 | 3.10 to under 3.40 |
| C | 4.10 to under 4.60 | 2.80 to under 3.10 |
| D | 3.60 to under 4.10 | 2.50 to under 2.80 |
These bands apply to air conditioners up to 12 kW other than portable single and double duct units, which are labelled on EER instead. Most good wall-mounted splits sold now are A++ or A+++ for cooling.
Real examples
Two comparable 3.5 kW wall units show how the numbers look in practice. Daikin's Perfera FTXM35R pairing has a SEER of 8.65, A+++, and an annual cooling consumption of 137 kWh on its label, according to Daikin's product flyer. Mitsubishi Electric's MSZ-LN35VG is listed at a SEER of 9.5 and a SCOP of 5.1, A+++ for both cooling and heating.
Both are at the top of the scale. The difference between them is small in pounds. The difference between either of them and an old unit with a SEER of 4 is not.
Turning SEER into a running cost
The label already does most of the work. Its annual cooling consumption is the unit's design cooling load multiplied by a reference 350 hours of full-output running, divided by its SEER. For a 3.5 kW unit:
| SEER | Label consumption per year | Cost at 26.32p per kWh |
|---|---|---|
| 8.5 (A+++) | 144 kWh | £37.93 |
| 6.1 (A++) | 201 kWh | £52.86 |
| 5.1 (A) | 240 kWh | £63.22 |
| 4.0 (older unit) | 306 kWh | £80.61 |
The price is Ofgem's average cap rate for 1 October to 31 December 2026. If you use the system more than the reference 350 hours, scale the figure up. For an hourly figure, divide the cooling output in kW by the SEER and multiply by your electricity price: a 3.5 kW unit at SEER 7.0 draws 0.5 kW at full output, about 13p an hour. Our guide to air conditioning running costs covers more examples, including heating.
SEER, EER and SCOP: which to compare
- For cooling, compare SEER. It reflects how the unit actually runs over a season, including part load.
- For heating, compare SCOP for the average season. If you are using the unit as a main heat source, it matters as much as SEER.
- Treat EER and COP with care. They are single test points and can make a unit look better or worse than it performs over a year.
- Compare like with like. Use figures from the same label or the same test standard, not a SEER from one brochure and an EER from another.
UK SEER versus US SEER
American SEER ratings, and the newer SEER2, use different units and different test conditions, so a US SEER of 20 cannot be compared directly with a UK SEER of 8.5. If you are reading an American buying guide, its SEER numbers do not apply to equipment labelled for the UK market.
What else affects real efficiency
A high SEER only delivers if the system is right for the room and looked after. An oversized unit short-cycles, an undersized one runs flat out, and dirty filters or coils cut airflow and efficiency. Inverter control is a large part of why modern seasonal figures are so much better than older fixed-speed units, and our guide to inverter air conditioning explains why. Regular air conditioning maintenance keeps a system close to its rated performance.
Questions people ask about SEER ratings
What is a good SEER rating in the UK?
On the UK energy label, 8.50 or more is A+++ and 6.10 to under 8.50 is A++. Most good wall-mounted splits sold now fall in those two classes. Anything below about 5.6 is in the lower A class or below.
What is the difference between SEER and EER?
EER is cooling efficiency at a single full-load test condition. SEER averages efficiency over a reference cooling season, including the part-load running where inverter units do best, so it gives a more realistic picture of annual energy use.
What is the difference between SEER and SCOP?
SEER measures seasonal cooling efficiency and SCOP measures seasonal heating efficiency. A reversible air conditioner has both on its energy label, and the heating figure is given for the average heating season.
Does a higher SEER save money?
Yes. For the same cooling, a higher SEER uses less electricity. On the energy label, a 3.5 kW unit at SEER 8.5 uses about 144 kWh a year against about 240 kWh at SEER 5.1, roughly £25 a year less at the October to December 2026 price cap.
Can I compare a UK SEER with an American SEER?
No. US SEER and SEER2 ratings use different units and test conditions, so the numbers are not comparable. Use the UK energy label or EN 14825 figures for equipment sold here.
Choosing an efficient system
Ask for the data sheet of every unit you are quoted and compare SEER, SCOP and indoor noise side by side. If you would like a recommendation for your rooms, see our home air conditioning installation service or ask us for a quote.
Last updated: 4 November 2026
Written by
Ali Elm
Ali is the Head of Operations at Be Cool Refrigeration with over a decade of hands-on experience in HVAC and commercial refrigeration. He oversees every installation, repair, and maintenance project, making sure the work meets the highest standards. Ali holds full F-Gas certification and has worked across residential, commercial, and industrial refrigeration systems throughout London and the South East. When he is not on site, he writes these guides to help business owners and homeowners understand their cooling systems better.