A mini-split is a type of heat pump that heats and cools without ducts. It has two main parts: a small outdoor unit (the compressor and coil) and one or more indoor units, usually mounted high on a wall. A thin bundle of refrigerant lines and wiring connects them through a small hole in the wall. Each indoor unit conditions the room it is in.
Because it is a heat pump, a mini-split both heats and cools — it moves heat outdoors in summer and indoors in winter. A single-zone system has one indoor unit for one room. A multi-zone system runs several indoor units off one outdoor unit, each with its own thermostat, so you condition only the rooms you are using. Most mini-splits use an inverter (variable-speed) compressor, which runs at low speed for steady comfort.
Mini-splits are the most common kind of ductless system, though some models connect to short runs of duct. They are efficient partly because they skip the energy lost in ducts. DOE-listed mini-splits reach SEER2 ratings from 15.2 up to 35.
For a buyer, a mini-split fits rooms a central system struggles with: additions, garages, attics, sunrooms, and older homes without ducts. In 2026 a single-zone install runs about $2,000 to $6,000, with multi-zone systems higher. The trade-offs are the visible indoor units and a higher cost per room than extending existing ducts, so the value is best when adding ducts would be costly.