An air conditioner’s cooling capacity is not the same as the electricity it uses. A modern inverter moves roughly three units of heat for every unit of electricity, so a 12 000 BTU (3.5 kW) aircon draws only about 1.1 kW at full output — and much less once the room is cool.
Running cost calculator
Work out your own cost
Cost = power (kW) × hours × your tariff per kWh. Find the power input (kW) on the specification sheet and your tariff on your municipal or Eskom bill — tariffs differ a lot between areas and change every year.
| Size | Power at full output | Typical inverter average | 8 hours at R3.50/kWh* |
|---|---|---|---|
| 9 000 BTU (2.6 kW) | about 0.8 kW | 0.3 – 0.6 kW | about R8 – R17 |
| 12 000 BTU (3.5 kW) | about 1.1 kW | 0.4 – 0.8 kW | about R11 – R22 |
| 18 000 BTU (5.3 kW) | about 1.6 kW | 0.6 – 1.1 kW | about R17 – R31 |
| 24 000 BTU (7.0 kW) | about 2.2 kW | 0.8 – 1.5 kW | about R22 – R42 |
*Estimates for an inverter with the room closed and the filters clean; R3.50 per kWh is an example tariff. Hot afternoons, open doors and lower set temperatures push the cost towards the top of the range. A fixed-speed unit typically costs more to run.
Ways to cut the running cost
- Set 24–25 °C in summer — see the best temperature.
- Choose an inverter for rooms you use every day.
- Close doors, windows and curtains on the sunny side.
- Clean the filters every few weeks — here’s how.
- Don’t oversize or undersize the unit: use the size guide.
- Use the timer or Wi-Fi so it isn’t cooling an empty room.
How many watts does a 12000 BTU aircon use?
About 1 100 watts at full output for a modern inverter, dropping to a few hundred watts once the room has cooled. Check the exact power input on the model’s specification sheet.
Does an aircon use a lot of electricity?
Less than most people expect. Once the room is cool, a bedroom inverter typically uses about 0.3–0.8 kWh an hour — roughly the same as boiling a full kettle four to eight times. Heating with an aircon also costs far less than an electric bar or oil heater.
Is it cheaper to leave an inverter aircon on all day?
In a room you use all day, letting an inverter run steadily at a sensible temperature is often cheaper than switching it off and making it pull a hot room down again. For rooms left empty for hours, switch it off or use the timer.