Built-in or central vacuum cleaners, also known as ducted vacuum cleaners, move the suction motor and bag to a central location in the building and provide vacuum inlets throughout the building: only the hose and pickup head need be carried from room to room, and the hose is commonly 8 m (25 ft) long, allowing a large range of movement without changing vacuum inlets. Plastic piping connects the vacuum outlets to the central unit. The vacuum head may either be unpowered or have beaters operated by an electric motor or air-driven motor.The dirt bag in a central vacuum system is usually so large that emptying or changing needs to be done less often, perhaps once per year. The central unit usually stays in "stand-by", and is turned on by a switch on the handle of the hose, or the unit powers up when the hose is plugged into the wall inlet when the metal hose connector makes contact with two prongs in the wall inlet and the current is transmitted through low voltage wires to the main unit. Such a unit also produces greater suction than common vacuum cleaners, because a larger fan and more powerful motor can be used when they are not required to be portable. Another benefit of a central vacuum system is that unlike a standard vacuum cleaner, which blows some of the dirt collected back into the room being cleaned (no matter how efficient its filtration), a central vacuum removes all the dirt collected to the central unit. Since this central unit is usually located outside the living area, no dust is recirculated back into the room being cleaned. In addition, because of the remote location of the motor unit, there is less noise in the room being cleaned than with a standard vacuum cleaner. Also it is possible on most newer models to vent the exhaust entirely outside with the unit inside the living quarters.