Glossary · Air conditioning
What is SEER?
SEER stands for Seasonal Energy Efficiency Ratio. It rates how efficiently an air conditioner or heat pump cools across a whole cooling season, not at one test point. The higher the SEER, the less electricity the unit needs for the same cooling. It is the cooling counterpart of SCOP, which rates heating.
Key points
- SEER measures cooling efficiency across a season. SCOP is the matching measure for heating.
- The government's Energy Technology List defines SEER as the ratio of total cooling capacity to the effective power input of the unit.
- Daikin says a higher SEER means a more efficient unit, with class A+++ at 8.5 or above and class A++ from 6.1 to 8.5.
- A SEER on the label is a test result. Daikin says real-world efficiency still depends on installation, insulation and maintenance.
- Correct sizing matters as much as the SEER figure, because an oversized or undersized unit wastes energy.
How SEER works
SEER is a seasonal rating for cooling. The government’s Energy Technology List defines the Seasonal Energy Efficiency Ratio as the ratio of the total cooling capacity to the effective power input of the unit.[1]DESNZ, Energy Technology List: Air to Water Heat Pumps In plain terms, it asks how much cooling you get for each unit of electricity, averaged over a typical cooling season.
Seasonal figures are used because an air conditioner rarely runs flat out. It spends most of its time at part load, so a single test point would say little. The Energy Technology List says its seasonal measures follow the BS EN 14825 standard for an average climate.[1]DESNZ, Energy Technology List: Air to Water Heat Pumps Heating has the matching measure, SCOP.
Reading the numbers
Daikin gives these bands for the energy label on air conditioners and air-to-air heat pumps.[2]Daikin UK, Air Conditioner Size Guide: Find the Right Unit
| Cooling class | SEER |
|---|---|
| A+++ | 8.5 or more |
| A++ | 6.1 to 8.5 |
Daikin adds that a SEER of 7.0 or higher typically represents top-tier performance and that most efficient systems range between 6.1 and 8.5.[2]Daikin UK, Air Conditioner Size Guide: Find the Right Unit It also says many of its modern inverter wall units reach SEER ratings above 7.5.[3]Daikin UK, Air conditioning types: best AC systems explained Those are one manufacturer’s figures. Always check the data sheet for the exact model, and see inverter air conditioners for why variable-speed units tend to score higher.
Example
Hardeep is choosing air conditioning for a loft bedroom in Bradford that overheats in summer. One quote is for a unit rated A++ for cooling. BASI’s page for its Bosch Climate 3200i lists it as A++ for cooling and A+ for heating.[4]BASI Heating, Air conditioning, supplied and fitted Hardeep compares the SEER on each data sheet, and also checks the capacity in kW. A unit with a higher SEER but the wrong size would still run poorly, so the capacity has to suit the room first. See air conditioning for how BASI quotes.
What people get wrong
Many people pick the highest SEER and stop there. The rating does not account for how the unit is sized or installed. Daikin says undersized units struggle to reach comfort levels, while oversized ones cycle on and off, which increases running costs and wear.
That is from Daikin’s sizing guide.[2]Daikin UK, Air Conditioner Size Guide: Find the Right Unit
A second mistake is to read SEER as a running cost. It is an efficiency ratio. Your bill depends on how many hours the unit runs, the temperature you set and your electricity tariff. Daikin also notes that real-world efficiency depends on installation, insulation and maintenance.[2]Daikin UK, Air Conditioner Size Guide: Find the Right Unit Look at the air conditioning running costs page for the wider picture.
The bottom line
SEER tells you how efficiently an air conditioner cools across a season. A higher number means less electricity for the same cooling, and the A+++ and A++ bands give a quick way to compare units. It is only one input. Correct sizing, a good installation and sensible use decide what you actually pay.
Common questions
What is a good SEER rating for an air conditioner?
Daikin says class A+++ means a SEER of 8.5 or more and class A++ means 6.1 to 8.5, and that a SEER of 7.0 or higher is typically top-tier. The best choice is still a unit sized correctly for the room.
What is the difference between SEER and SCOP?
SEER rates cooling efficiency over a season. SCOP rates heating efficiency over a season. A reversible air conditioner that heats and cools carries both figures on its energy label.
Does a higher SEER always mean lower bills?
Not always. Daikin says real-world efficiency depends on installation, insulation and maintenance, and that oversizing leads to higher running costs and noisy operation. SEER is a test result, not a guarantee.
Is SEER measured in the same way for every unit?
Seasonal ratings are measured to a standard. The Energy Technology List says its seasonal metrics follow BS EN 14825 for an average season, which lets units be compared on the same basis.
Sources
We cite the original source for every figure: government, regulators, standards bodies and manufacturers' own documents. Each one shows the date we last checked it.
- DESNZ. Energy Technology List: Air to Water Heat Pumps. Checked 11 November 2026. ↩
- Daikin UK. Air Conditioner Size Guide: Find the Right Unit. Checked 11 November 2026. ↩
- Daikin UK. Air conditioning types: best AC systems explained. Checked 11 November 2026. ↩
- BASI Heating. Air conditioning, supplied and fitted. Checked 11 November 2026. ↩