A split air conditioning system puts the compressor and condenser outside the building and the evaporator and fans inside the building. In a central air conditioning system, fans push cooled air from a centrally located evaporator through ducts to the entire building. In a ductless split system, fans in a wall-mounted unit move the air from the evaporator into the room in much the same way that a window unit does. Because the split unit’s noisy compressor is outside, however, a split ductless system is much quieter than a window unit.

Split units are efficient, but because they require the installation of equipment outside the building, they might not be suitable for high-density residential areas, such as apartments in urban areas.