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 A/C 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.