Two aircons with the same BTU rating can use quite different amounts of electricity. The efficiency ratings on the specification sheet tell you which one costs less to run.
| Rating | What it measures | Higher is… |
|---|---|---|
| EER | Cooling output ÷ electricity input at full load | Better |
| SEER | Cooling efficiency averaged over a whole season, including part-load running | Better |
| COP | Heating output ÷ electricity input | Better |
| SCOP | Heating efficiency over a season | Better |
An EER of 3.2, for example, means the unit delivers 3.2 kW of cooling for every 1 kW of electricity. Seasonal ratings (SEER and SCOP) are the best guide to real running costs because aircons spend most of their time at part load — which is exactly where inverter units shine.
Energy labels
Many split units sold in South Africa carry an energy-efficiency label from A (most efficient) to G. Compare labels between models of the same size, and look at the power input in kW to estimate your running cost.
What is a good SEER rating for an aircon?
Compare models of the same size: inverter units have much higher seasonal ratings than fixed-speed units, and the highest-rated models cost noticeably less to run in rooms used every day.
Is a higher BTU less efficient?
Not necessarily. Efficiency is about output per unit of electricity, not size. But an oversized unit cycles on and off and wastes energy, so buy the size the room needs.