Sometimes called mini split-system air conditioners, a ductless air conditioner add-on unit has an outdoor compressor/condenser section and an indoor air-delivery component. The two sections are connected by a conduit housing that contains the power connection, tubing for the refrigerant and a condensate drain.
Ductless air conditioners can be mounted on ceilings or sidewalls, and they work well for cooling individual rooms or in apartments and condos when installing ductwork is too expensive. These mini-split systems are also ideal for homes that were built before central heating and air conditioning were commonplace. Installing traditional ductwork in these properties, particularly if they are designated as heritage homes, is sometimes not an option.
Some mini-split models can run up to four air-delivery units using one outdoor compressor section. Since each air-delivery unit has its own thermostat, there's no need to heat or cool an unoccupied room, which saves energy.
Comparing mini-split air conditioners with traditional window units, the former is more efficient at keeping a room at a constant temperature because of the thermostat. Since the mini-split is mounted inside the home instead of in a window, it doesn't have to be moved during the colder seasons. Ductless air conditioners are more expensive than window units, and depending on the model, they can be pricier than a central air conditioner.