What Is a Mini-Split and How Does It Work?

A mini-split is a heat pump that delivers heat and air conditioning without ductwork. An outdoor unit connects to one or more indoor units through a small bundle of refrigerant lines and wiring that passes through a small hole in the wall, typically about three inches across.

How It Heats and Cools

In cooling mode, the system moves heat from inside the house to the outdoor unit, like an air conditioner. In heating mode it reverses and moves heat from the outdoor air into the house. Because it moves heat instead of burning fuel, it runs on electricity alone.

The Parts of a Mini-Split

• Outdoor unit: the compressor and outdoor coil.
• Indoor units: wall-mounted heads, ceiling cassettes or concealed ducted units, each with its own control.
• Line set: the refrigerant lines, drain and wiring between them.

Which Homes It Suits

Mini-Split vs. Window Unit

A window or portable air conditioner sits in the room with its compressor, which makes it loud and blocks the window. A mini-split puts the compressor outside, so the indoor unit is quiet. It also heats, which window units usually do not.

Mini-Split vs. Central Heat Pump

Both are heat pumps. A central heat pump moves air through ducts from one indoor air handler. A mini-split delivers air directly from each indoor unit, so it needs no ducts and each area can run at its own temperature. Read heat pump vs. mini-split.

Care and Lifespan

The indoor filters slide out for cleaning by hand. A yearly professional tune-up checks the refrigerant charge, coils and both operating modes, and keeps the manufacturer warranty valid.

Mini-splits fit homes without ductwork, additions, in-law units and rooms that need their own temperature. Many 1920s–1940s Bay Area homes were built without ducts. Single-zone installs start at $6,500. Read mini-splits for homes without ducts.