Consider replacing your old air conditioner with a new efficient model. With higher electricity prices replacing your old air conditioner may make economical sense.
Refer to our this article on making your house naturally cooler. You may actually find that you don't really need to have an air conditioner after all.
Ducted air conditioning systems are more energy efficient than room air conditioners if cooling a whole house. However, if you would only cool one or two rooms it would probably be cheaper to use a room unit or split system.
If you opt for the room air conditioner, you must choose between a wall-mounted and a window mounted model. Split systems are more popular now that the wall mounted systems where a large whole was made in a wall. Window systems are an option but are not as efficient as a split system air-conditioner.
The next step is very important: get the right size unit for your needs. If you install an air conditioner larger than you need, it will run for shorter periods and cycle on and off more frequently. Result: higher electricity bills.
It also won't dehumidify as much so you won't feel as comfortable and will set the temperature even lower. Interestingly a good quality Fujitsu Inverter Air Conditioner when running in a medium sized room at the right size is very quiet and does not drop the temperature hugely but the comfort level in the room is fantastic especially for more humid areas (Brisbane in summer). Inverters can vary the speed of the compressor ? they don't run flat out and stop like older conventional air conditioners.
Don't accept the simple rules of thumb by a salesperson because there are many factors that affect the size requirements for air conditioning -:
You need a qualified air conditioning technician to help with these choices (not a washing machine salesman) at your local outlet.
Choose an efficient quiet system with check this article on how to compare air conditioners. This shows how to check the energy rating of air conditioners sold in Australia.
Avoid a cheaper copycat air conditioner. Quality brands like Fujitsu and Mitsubishi are constructed to create less noise. Their engineers ensure the unit is well balanced to reduce vibration.