A mono-split air conditioner consists of two units: an outdoor unit that is always installed outside the building on special wall or floor brackets; an indoor unit that can be of the split wall, floor console, built-in cassette or ducted type. Single-split systems are used for air-conditioning a single room, unlike multi-split systems (dual, trial, quadri or penta) which can air-condition several rooms at the same time using a single external unit.