All about air conditioners

Air conditioners are highly effective at lowering air temperatures and also help reduce humidity. In recent years, cheaper, more efficient models have become available, including compact reverse-cycle units that also provide heating. But air conditioners are still the most expensive cooling systems.

These systems work by drawing air through a water-moistened filter to cool it. The cool air is then blown through the house. Available as portable, fixed-unit or ducted systems, they are fairly inexpensive and use relatively little energy, but can be noisy, obtrusive and use a lot of water.

• Before buying, consider your local climate. Evaporative coolers work more efficiently in areas where the average relative humidity is low.
• For a room of under 25 square metres (270 square feet), you can use a portable model. Fixed units will cool a room of up to 50 square metres (540 square feet), but can cost five times as much.
• On portable units, look for directional shutters, variable speed settings and a water-level gauge – all will help you monitor and increase the efficiency of the system.
• When cooling, keep windows and doors open to let damp air out.
• Install the unit on the side of the house facing prevailing warm winds. That way, you can block the warm air and open the windows on the other side to let moisture out.
• If the weather is particularly humid, turn the water supply off and use just the fan.
• During cold weather, cover your roof unit and close vents to stop heat escaping.

• Split systems, which have separate indoor and outdoor elements linked by piping, are generally cheaper, quieter and use less energy than fixed units, which consist of a box mounted on a window or outside wall. Ducted systems use the most energy and are the most expensive to buy and run.
• As a rule of thumb, you'll need a system with 100–140 watts (0.1–0.14 kW) per square metre of living room and 80–100 watts (0.08–0.1 kW) per square metre of bedroom, depending on your climate and house design. Discuss with your supplier.
• Select units with a high Energy Rating. They may cost a little more but will soon pay for themselves. Each extra star means a saving of about 10 per cent in running costs.
• If you opt for a ducted system, choose one with zoning – the ability to switch cooling on or off in different parts of the house. This will minimize energy use and costs.
• Select a model with a programmable timer and thermostat, economy settings and adjustable speeds and louvres.
• Install the unit out of direct sunlight and don't block its outlet with furniture or curtains.
• For maximum efficiency, shut doors and windows in the room where the unit is operating.
• Don't set the thermostat too low (26–27°C (78-80°F) should be cool enough), and remember to turn it off when you go out.
• Clean the filters regularly and keep coils and fans free of dust.