In the heat of summer, an air conditioner is essential for keeping your home as comfortable as it should be. Window and wall unit air conditioners, once installed, are compact, cost effective and useful in both houses and apartments. A split system air conditioner offers discreet operation, comprising two parts: one unit indoor and one outdoor. Many of these systems have reverse cycle capability, meaning they can also heat. If you'd prefer a system with no installation, a portable air conditioner can function simply in any room with a window.