Ductless, Mini-Split Heating and Air Conditioning Systems
Mini-Splits have numerous potential applications in residential, commercial, and institutional buildings. The most common applications are in multifamily housing or as retrofit add-ons to houses with "non-ducted" heating systems.  They can also be a good choice for room additions and small apartments, where extending or installing distribution ductwork (for a central air-conditioner or heating systems) is not feasible.

Two Main Components
Like central systems, mini splits have two main components: an outdoor compressor/condenser, and an indoor air-handling unit. A conduit, which houses the power cable, refrigerant tubing, suction tubing, and a condensate drain, links the outdoor and indoor units.

Advantages

• The main advantages of mini splits are their small size and flexibility for zoning or heating and cooling individual rooms.

• Ductless mini split systems are also often easier to install than other types of space conditioning systems. For example, the hook-up between the outdoor and indoor units generally requires only a three inch (~8 centimeter [cm]) hole through a wall for the conduit. Also, most manufacturers of this type of system can provide a variety of lengths of connecting conduits. So, if necessary, you can locate the outdoor unit as far away as 50 feet (~15 meters [m]) from the indoor evaporator. This makes it possible to cool rooms on the front side of a building house with the compressor in a more advantageous or inconspicuous place on the outside of the building.
•  Since mini splits have no ducts, they avoid the energy losses associated with ductwork of central forced air systems. Duct losses can account for more than 30% of energy consumption for space conditioning, especially if the ducts are in a unconditioned space such as an attic.
• In comparison to other add-on systems, mini splits offer more flexibility in interior design options. The indoor air handlers can be suspended from a ceiling, mounted flush into a drop ceiling, or hung on a wall.
• Split-systems are quieter than traditional thru-wall or window mounted room air-conditioners because the compressor/condenser unit is installed “outside” the living area.
•  Split-systems can also help to keep your home safer since there is only a small hole in the wall. Window mounted room air-conditioners can provide an easy entrance for intruders.

Suitable for: Room Additions ~ Garage Apartments ~ Finished Basements ~ Motel Rooms ~ Restaurants ~ Home Offices ~ Workshops ~ and a host of other applications where ducted systems would be difficult to install.

Qualified installers and service people for mini splits may not be easy to find. In addition, most conventional heating and cooling contractors have large investments in tools and training for sheet metal duct systems. They need to use (and charge for) these to earn a return on their investment, so they may not recommend ductless systems except where a ducted system would be difficult for them to install.