A ductless mini-split air conditioner, often called a "mini-split AC," provides cool air through an outdoor compressor and condenser joined to multiple indoor air distributor units. The mini-split takes its name from the small size of the indoor units, several of which can be connected to one outdoor compressor.
Often chosen for industrial use or in multi-dwelling residential buildings where a central air conditioning system or window AC units are not practical, the mini-split's outdoor portion cools and conditions ambient air, sending it through small conduits to independent indoor air distribution systems smaller than the typical window AC.
Unlike central air conditioners, mini-split systems require no ducting, which saves on installation costs and helps minimize energy losses. The conduits by which air is transmitted from the outdoors to the indoor units can be installed through small cut-outs as little as 3 inches wide through a building's exterior walls. Further adding to potential energy savings, a single indoor "split" powers a single room with its own dedicated thermostat, allowing the user to cool and condition only the areas of the home or workspace currently being used.
Installation options include hanging the indoor unit from the ceiling, building it into a recessed ceiling, or placing it along a wall. Direct access to the outdoors, other than through the attached conduits, is not necessary.
However, mini-split systems are typically twice the price of simpler window-mounted AC units, and can be more expensive than even central air systems. They also require a place to collect water condensation running off the outdoor condenser, as well as the drilling of several holes into the side of a building.