An over-the-range vent is used in kitchens to expel the smoke, grease and steam vapors that are released during the cooking of food products on ranges. An exhaust fan captures the unwanted vapors and releases them through the vent.
If the hood is meant to expel grease vapors in addition to steam, then a grease filter needs to also be installed. A common way to describe vents is by their air flow, which is usually measured by cubic feet per minute. Small over-the-range vents can be used in residential applications while commercial kitchens require much larger vents due to the considerably greater volume of food involved.