What is the definition of a mini split unit heat and air? A mini split unit is a type of heating and air air conditioning system that uses individual air handlers to provide heating and cooling in separate rooms or areas. The mini split system is advantageous in that it allows for zoning, or the ability to control individual room temperatures. This is done by having an outdoor unit connected to multiple indoor air handlers via refrigerant lines. The outdoor unit contains the condenser and the compressor, while the indoor unit contains the evaporator. The outdoor unit is responsible for the transfer of heat from inside to outside and the indoor unit is responsible for cooling the air in the room. The mini split system is typically more energy efficient than traditional central air conditioning systems because it only cools or heats the areas that are being used at that time. The mini split system also doesn’t require a duct system, which can save on installation costs.