Choosing an air conditioner is not a matter of buying the biggest unit that fits the budget. Capacity has to match the room, the heat load inside it and the way the space is used. Get it wrong and you live with the consequences for the life of the unit.
What the kW rating actually means
The cooling capacity printed on a unit is the amount of heat it can remove, expressed in kilowatts. As a rough starting point for a well-insulated South African home with a standard ceiling height:
- 2.5 kW for a small bedroom or study up to roughly 12 square metres.
- 3.5 kW for a typical main bedroom or small lounge of about 18 square metres.
- 5.0 kW for a living area of about 25 to 30 square metres.
- 7.1 kW and above for open-plan living spaces, large home offices or rooms with heavy sun exposure.
Treat those numbers as a starting point only. A north or west-facing room with large unshaded glass, a room above a garage roof, or a space with a server cabinet or home gym equipment needs more capacity than its floor area suggests.
Why an oversized unit is a problem
An oversized unit reaches the set temperature quickly and switches off, then starts again a few minutes later. This short cycling never runs long enough to remove humidity, which leaves the room feeling cold and clammy, and it wears the compressor with constant starting current. Inverter units modulate their output, which softens the effect, but the capacity still has to be in the right range.
Inverter versus fixed-speed
Inverter units vary compressor speed to hold a stable temperature. They cost more upfront, run more quietly and typically use less electricity over a cooling season. For a room used daily through summer, the inverter premium usually justifies itself. For a guest room used a few weeks a year, a fixed-speed unit can still make sense.
Installation quality matters as much as the badge
Correct pipe sizing, a properly evacuated and pressure-tested line set, adequate drainage fall and a condenser sited where it can breathe all affect performance. A premium unit installed poorly will underperform a mid-range unit installed correctly.
Legacy Air supplies and installs correctly sized residential and commercial systems across Mulbarton and greater Johannesburg, and provides a free written quotation with the recommended capacity and unit options explained before you commit.