With electricity prices rising every year, it’s a fair question before you buy: what will an aircon actually cost to run? The answer depends on the size of the unit, whether it’s an inverter, how long it runs and what you pay per kWh.
This guide breaks it down with real numbers, so you can work out what an air conditioner will add to your monthly bill.
BTU vs kW: What the Numbers Mean
Air conditioners in South Africa are sold by BTU (British Thermal Units), such as 9,000, 12,000, 18,000 or 24,000 BTU. BTU measures cooling capacity: how much heat the unit can remove from a room in an hour.
Your electricity bill is measured in kWh. That is the power the unit draws multiplied by the hours it runs.
The two are not the same thing:
- 12,000 BTU equals about 3.5 kW of cooling output.
- That same unit typically draws only around 1.0–1.2 kW of electricity at full load.
This works because an air conditioner moves heat rather than creating it. A good unit delivers about three units of cooling for every one unit of electricity it uses. The measure for this is the unit’s EER (cooling) or COP (heating). The higher the number, the cheaper the unit is to run.
Tip: Check the spec sticker on the indoor unit or the product sheet for “rated power input” in kW or W. That’s the figure that matters for your bill.
How Much Does an Aircon Cost to Run Per Hour?
The formula is simple:
Power input (kW) × hours used × your tariff (R/kWh) = running cost
Here are typical full-load figures for common midwall split sizes at R3.80/kWh:
| Unit size | Typical power input | Cost per hour (full load) |
|---|---|---|
| 9,000 BTU | ±0.8 kW | ±R3.04 |
| 12,000 BTU | ±1.1 kW | ±R4.18 |
| 18,000 BTU | ±1.65 kW | ±R6.27 |
| 24,000 BTU | ±2.2 kW | ±R8.36 |
These are worst-case numbers. Once the room reaches the set temperature, the compressor slows down or switches off, so the real hourly cost is usually lower.
Worked example: a bedroom aircon in summer
Say you have a 12,000 BTU aircon running 6 hours a night for 30 days. On average, the compressor works at about 70% of full load.
- 1.1 kW × 70% = 0.77 kW average
- 0.77 kW × 6 hours × 30 days = 139 kWh per month
- 139 kWh × R3.80 = about R528 per month
Your own tariff, how well the room is insulated and the temperature you set will move this number up or down. Tariffs also differ between municipalities and Eskom-direct supply, so check the rate on your own bill or prepaid slip.
Inverter vs Non-Inverter: Which Uses Less Electricity?
This is where the biggest savings are.
Non-inverter air conditioners run their compressor at one fixed speed. They switch on at full power, cool the room past the set point, switch off, then restart at full power when the room warms up again. Every restart draws a surge of power.
Inverter air conditioners vary the compressor speed. They work hard to cool the room quickly, then throttle down and hold the temperature at low power instead of switching on and off.
In practice, this means:
- Inverters use noticeably less electricity when run for long periods, often around a third less, depending on how the unit is used.
- Inverters hold a steadier temperature, with no hot-cold swings.
- Inverters are quieter, because the compressor isn’t constantly starting and stopping.
- Non-inverters cost less upfront, so they still make sense for rooms used only occasionally, such as a guest room or a boardroom used once a week.
If the aircon will run for several hours a day, an inverter usually pays back its higher purchase price through lower electricity bills. Browse our air conditioners for sale or the midwall split air conditioner range to compare inverter models from Samsung, Alliance, LG, Carrier and Midea.
Does Aircon Size Affect Electricity Use?
Yes, and getting it wrong in either direction costs you money:
- Too small: the unit runs flat out for hours and never quite reaches the set temperature.
- Too big: a non-inverter switches on and off constantly. An oversized inverter costs more to buy and draws more than it needs to.
The right size depends on:
- room dimensions
- ceiling height
- sun exposure
- insulation
- how many people use the space
Our air conditioner installers work this out during a site assessment, so you don’t pay for capacity you don’t need. The installers’ work matters too: correct pipe lengths, a good seal and the right position all affect how efficiently the system runs.
7 Ways to Cut Your Aircon’s Electricity Use
- Set it to 23–25°C in summer. Each degree cooler makes the unit work harder. 18°C is rarely needed and costs a lot more.
- Close doors and windows. You’re paying to cool the room, not the passage or the garden.
- Block direct sun. Blinds or curtains on sun-facing windows reduce the heat the aircon has to remove.
- Insulate the ceiling. In Gauteng homes, a hot roof space is one of the biggest sources of heat gain. Good insulation makes any aircon cheaper to run.
- Use the timer. Switch the unit on 15–20 minutes before you need the room, not all day.
- Keep the filters clean. Clogged filters restrict airflow and make the compressor work harder.
- Service it regularly. A professional aircon service cleans the coils, checks the refrigerant and catches small faults before they hurt efficiency.
Frequently Asked Questions
How many kWh does an aircon use per day?
A 12,000 BTU unit running 8 hours a day typically uses about 6–9 kWh, depending on whether it’s an inverter and how hard it has to work. Larger units use proportionally more.
Is it cheaper to leave an inverter aircon on all day?
For rooms in constant use, an inverter left on at a moderate temperature can use less power than one switched on and off repeatedly. That’s because it avoids the high-power pull-down each time it restarts. For rooms empty for long periods, switching off is still cheaper.
Does an aircon use more electricity on heating mode?
Heating mode is often very efficient. A heat-pump aircon typically delivers about three times more heat than the electricity it uses, which makes it cheaper to run than most plug-in heaters.
How do I find my aircon’s power consumption?
Look for “rated power input” on the sticker on the indoor or outdoor unit, or in the product manual. It’s listed in watts (W) or kilowatts (kW). 1,000 W = 1 kW.
What size air conditioner do I need?
The right size depends on the room’s dimensions, ceiling height, sun exposure, number of people and how the space is used. An undersized unit struggles to cool, and an oversized one wastes electricity. Our installers work out the correct capacity during the site assessment.
Looking for an energy-efficient air conditioner? Alair supplies, installs and services inverter air conditioners across Gauteng. Call 0860 886 886 or request a quote.