Too small
The unit runs flat out all afternoon, never quite reaches the temperature you set, uses more electricity and wears out sooner.
Buying guide
What size aircon do I need?
Most rooms need about 600 BTU of cooling for every square metre of floor, then more for afternoon sun, a hot roof or a busy kitchen. Use the calculator below for a starting size, then we confirm it on site before anything is ordered.
Sizing calculator
Find your starting size.
Measure the room's length and width in metres. If you know the floor area already, type it straight into the area box.
This is a general guide for one room cooled by one wall-mounted split unit. Open-plan spaces, offices, server rooms and medical or technical spaces need a proper heat-load calculation. Ask us for one.
Quick reference
Common aircon sizes by room size.
For an average room in Gauteng with a standard ceiling and some sun. Add one size up for strong afternoon sun, an uninsulated roof or a kitchen.
| Unit size | Cooling output | Room size | Typical room |
|---|---|---|---|
| 9,000 BTU | About 2.6 kW | Up to 15 m² | Small bedroom or study |
| 12,000 BTU | About 3.5 kW | 15 to 20 m² | Main bedroom or small office |
| 18,000 BTU | About 5.3 kW | 20 to 30 m² | Lounge or open office corner |
| 24,000 BTU | About 7 kW | 30 to 40 m² | Open-plan lounge and dining room |
| 30,000 to 36,000 BTU | About 8.8 to 10.5 kW | 40 to 60 m² | Large open-plan area, small shop |
| Bigger than 36,000 BTU | Over 10.5 kW | Over 60 m² | Usually a cassette, ducted or multi-unit system |
Why size matters
Too small and too big both cost you.
Too big
The room cools fast, then the unit keeps switching off before it has pulled the moisture out of the air. The room feels cold and clammy, and the extra size costs more to buy.
About right
The unit runs steadily, holds the temperature, controls humidity and lasts longer. An inverter unit sized correctly is the quietest and cheapest to run.
After size
Four other things to decide.
Inverter or fixed speed
An inverter unit slows down once the room is cool instead of switching on and off, so it uses less electricity and keeps the temperature steadier. It costs more up front and usually pays that back if the unit runs most days. A fixed-speed unit can make sense for a room you only cool now and then.
Type of unit
- Mid-wall split: the usual choice for bedrooms, lounges and offices.
- Cassette: sits in the ceiling and spreads air four ways. Good for shops and open offices.
- Under-ceiling: for large rooms without a ceiling void.
- Ducted: one hidden unit feeding several rooms through vents.
- Multi-split: one outdoor unit running two to five indoor units.
Where it goes
The indoor unit should blow along the length of the room, not straight onto a bed or desk. The outdoor unit needs space around it to breathe, a solid mounting, and a short, neat pipe run to the indoor unit. Noise matters too: keep the outdoor unit away from bedroom windows, yours and your neighbours'.
Who installs it
A good unit badly installed will leak, drip or fail early. Ask your installer whether they are SAQCC Gas registered for refrigerant work, whether they issue a completion certificate, and how they record the unit's make, model and serial number for the warranty.
How we help
We confirm the size before you buy.
Send us the calculator result, a photo of the room and a photo of where the outdoor unit could go. We check the size, recommend a unit and tell you what the installation involves. As approved installers for Midea, Daikin, Sinclair and Carrier, we can match the unit to your budget and the room.
Every installation is recorded with make, model, serial number and location, and comes with a completion certificate and workmanship warranty.
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