The Ductless mini split air conditioner has two units: the compressor which sits outside of the home, and the air handler which is placed inside. Like any AC you need to know how many BTUs are needed for the area you are trying to cool - heat. A mini split air conditioner is very quiet and efficient, but it is more expensive than a window or portable air conditioner. Since they are ductless, the mini split AC/Heaters avoid the energy losses associated with the ductwork of central forced air systems.