What is a ductless mini split and how exactly do they work? A ductless mini split system, in its most basic form, includes one outdoor unit and one indoor unit, connected by refrigerant tubing and electrical wiring. The indoor unit is often wall-mounted and delivers heated or cooled air directly into the living space – no ductwork needed. This is called a single-zone system and it’s designed to provide heating and cooling comfort to one specific area. A Carrier ductless multi-zone system combines one outdoor unit with up to five indoor units to provide comfort for an entire home.