This type of unit is very popular overseas where many buildings do not have ductwork. They are becoming popular in the US where homes need to be cooled but no ductwork exists, such as in the case of homes heated with boilers (see Boilers).

The system has an outside condensing unit, very similar to a regular split system air conditioner. It also has copper tubing running to an indoor unit. However, the indoor unit(s) (It can have multiple indoor units with one outdoor unit) are not ducted, they simply hang on a wall or mount in the ceiling. These are not put in a window – like the window air conditioner, and they don’t need a huge hole in the wall – like the PTAC unit. They are much quieter than window units, because the noisiest part of the system is outside. Another advantage is the ability to have multiple indoor “blower” units, giving you air conditioning in more than one room.