A kitchen hood, exhaust hood, or range hood is a device containing a mechanical fan that hangs above the stove or cook top in the kitchen. It removes airborne grease, combustion products, fumes, smoke, heat, and steam from the air by evacuation of the air and filtration in commercial kitchens exhaust hoods are often used in combination with fire suppression devices so that fumes from a grease fire are properly vented and the fire is put out quickly. Commercial vent hoods may also be combined with a fresh air fan that draws in exterior air, circulating it with the cooking fumes, which are then drawn out by the hood. In most exhaust hoods, a filtration system removes grease (the grease trap) and other particles. Although many vent hoods exhaust air to the outside, some recirculation of the air to the kitchen. In a recirculation system, filters may be used to remove odors in addition to the grease.