Mini-Split systems make good retrofit add-ons to houses without ducts. Due to their lack of ducts, Mini-Splits avoid the energy losses associated with the 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 an unconditioned space such as an attic.

The main advantages of Mini-Splits are their small size and flexibility for zoning or heating and cooling individual rooms. Many models can have as many as four indoor air-handling units (for four zones or rooms) connected to one outdoor unit. This can be affected by how well the building is insulated and air sealed. Each of the zones has its own thermostat, so you only need to condition occupied spaces, which can save energy and money.

Ductless Mini-Split systems are easier to install. A Mini-Split system can provide a variety of lengths of connecting conduits, and, if necessary, you can locate the outdoor unit as far away as 50 feet from the indoor evaporator. This makes it possible to condition rooms on the front side of a house, but locate the compressor in a more advantageous or inconspicuous place on the outside of the building.

The cost of installing Mini-Splits can be higher than some systems, although lower operating costs and rebates or other financial incentives offset the initial expense.