Choosing the right aircon size is the most important decision you will make, and the one most often got wrong. A unit that is too small never cools the room; one that is too big wastes power and leaves the air clammy. Here is how to get it right for a Cape Town home.
As a starting point, small bedrooms suit 9,000 BTU, larger bedrooms and studies 12,000 BTU, and open-plan living areas 18,000 to 24,000 BTU. Go a size up for north- or west-facing rooms, rooms under uninsulated roofs, big glass doors, high ceilings and hot inland suburbs such as Durbanville, Bellville or Paarl. A site visit or good photos confirm the size.
What BTU means
Aircon cooling capacity is usually given in BTU (British Thermal Units) per hour. Common home sizes in South Africa are 9,000, 12,000, 18,000 and 24,000 BTU. The number tells you how much heat the unit can remove from a room each hour. Bigger rooms, and rooms that gain more heat from the sun, need more BTU.
A simple sizing table
These are starting points for a room with a standard ceiling height and average windows:
- Up to about 15 square metres: 9,000 BTU
- About 15 to 25 square metres: 12,000 BTU
- About 25 to 35 square metres: 18,000 BTU
- About 35 to 50 square metres: 24,000 BTU
- Larger open-plan spaces: two units, or a larger system
Then adjust for the factors below.
Things that push the size up
Sun and orientation
North-facing rooms get sun most of the day; west-facing rooms take the hot afternoon sun. Both need more capacity than a shaded south-facing room.
Glass
Large windows and sliding doors let in a lot of heat. Many Cape Town homes are designed around views of the mountain or the sea, with big glass frontages that need extra cooling.
Roofs and ceilings
Rooms under flat roofs, corrugated iron or uninsulated ceilings heat up fast. Double-volume spaces and high ceilings in older Southern Suburbs homes have more air to cool.
Where you live
Cape Town's suburbs vary a lot. The Atlantic Seaboard is cooled by the sea; Durbanville, Bellville, Brackenfell, Kuils River and the Winelands get much hotter summers. Homes inland usually need the larger end of each range.
How the room is used
Kitchens, home offices with computers and lounges where the family gathers have more heat from people and equipment.
Things that let you size down
- Shaded, south-facing rooms
- Good ceiling insulation
- Thick walls and small windows
- Coastal homes cooled by the sea breeze
Why oversizing is a problem too
It is tempting to buy a bigger unit to be safe. But an oversized unit cools the room so quickly that it switches off before it has removed much humidity. The room feels cold and clammy, the unit cycles on and off and efficiency drops. Inverter units cope better with slight oversizing, but correct sizing is still best.
Heating in winter
Most split units sold today are reverse-cycle, so they heat as well as cool. In Cape Town's wet winters this is a real benefit. A unit sized correctly for summer cooling will usually heat the same room well in winter.
Cape Town examples
- Sea Point one-bedroom flat: bedroom about 12 square metres, sea-facing with a breeze. 9,000 BTU.
- Rondebosch family home main bedroom: about 18 square metres, north-facing, high ceiling. 12,000 BTU, possibly 18,000.
- Durbanville open-plan lounge: about 40 square metres, west-facing sliding doors. 24,000 BTU or two 12,000 BTU units.
- Stellenbosch study: about 14 square metres, computers, afternoon sun. 12,000 BTU.
These are illustrations, not quotes. Every room is different.
Get it confirmed
The surest way to get the right size is a site visit or clear photos and measurements. We look at the room, windows, orientation and roof, then recommend a size. Every installation comes with a 2-year warranty and a free service every six months for those two years.
Frequently asked questions
Is a 9,000 BTU aircon enough for a bedroom?
For a small to medium bedroom without much sun, usually yes. Larger, sunny or inland bedrooms may need 12,000 BTU.
Should I buy an inverter aircon?
For rooms cooled or heated for more than a couple of hours a day, yes. Inverters use less electricity and run quieter.
Can one big aircon cool my whole house?
A single wall unit cools the room it is in, not a whole house. Larger spaces need multiple units or a different system.
A1 Refrigeration is an independent company and is not affiliated with or authorised by any appliance manufacturer. This guide is general advice. For anything involving electricity or refrigerant gas, use a qualified technician.
Need a hand? See our aircon installation service in Cape Town.