An Extractor Hood is a device which contains a mechanical fan and hangs above a cooker or stove in a kitchen in order to remove steam, smoke, airborne grease, odours and heat using a combination of filtration and evacuation of the air. It consists of three main components which are a hood or skirt to capture the rising gases, one or more grease filters and a fan or tangential blower for forced ventilation. There are two basic designs of hoods, being ducted or ductless. In a ducted application the unwanted air is ducted outside the building. In a ductless system the air dissipates within an activated charcoal filter before releasing it back into the kitchen. A ducted system is considered to be more efficient because the air is taken away from the indoor environment and released into the atmosphere, as well as eliminating the need to constantly replace filters. Extractor hoods almost always provide some kind of built in lighting to illuminate the cooking surface and utensils whilst cooking. They are typically electronically controlled, some high end models offering such features as remote control, motorised height adjustment, thermal sensor, overheat protection, boost mode, delayed shut off, filter cleaning reminder, temperature display and user presets.