The definition of a central heating and air system is one that is used to heat and cool a home or building. It is a system that uses a central unit to provide air conditioning and heating throughout the entire structure. This central unit is typically connected to a network of ducts that run throughout the building and are connected to vents in each room. The central unit is powered by either an electric or gas furnace and is responsible for controlling the temperature of the air that is circulated throughout the building. The central unit also controls the humidity levels and the amount of air that is circulated throughout the building. The central unit is typically connected to a thermostat that is used to set the desired temperature in each room. Central heating and air systems are a great way to maintain a comfortable environment in a home or building. They are energy efficient and provide consistent temperatures throughout the building.