The most common mistake we see is a unit that is too big for the room. It usually comes from a kind thought: get the next size up, just to be safe. It does not work that way, and it costs you money twice, once at purchase and again on every bill.
Why bigger is not better
An air conditioner does two jobs. It lowers the temperature and it pulls moisture out of the air. Drying the air takes time, with the coil cold and air passing over it steadily. An oversized unit hits the set temperature in a few minutes and backs right off, before it has removed much moisture. The room ends up cold but clammy, and you turn it down further to feel comfortable.
It also cycles up and down more often, which is harder on the compressor and noisier. In a bedroom, a big unit pushing a lot of air is the last thing you want at 2 am.
Why too small is a problem as well
An undersized unit runs flat out on a 38 degree day and never quite gets there. It is loud, it uses a lot of power and it wears out sooner. The aim is a unit that reaches temperature comfortably, then settles to a quiet, low speed and holds it.
A rough guide by room
- Bedroom, up to about 20 square metres: 2.5 to 3.5 kW
- Living room, 30 to 45 square metres: 5 to 7 kW
- Open-plan living and kitchen, 45 to 60 square metres: 7 to 9 kW
Treat those as a starting point. Floor area is only one part of the sum.
What changes the answer
- Insulation. An uninsulated ceiling can add a full size.
- Ceiling height. A 3 metre ceiling means a lot more air to cool.
- West-facing glass. Afternoon sun through a big window is a heater.
- Open doorways and stairwells, which let the air escape.
- Kitchens, which add heat from cooking and appliances.
This is why we do not size from a floor plan. Two living rooms with the same floor area can need quite different units, depending on which way the windows face and what is above the ceiling. A site visit takes about half an hour and it settles the question.
If you would like a room sized properly, send us the details and we will come and measure it.