A kitchen hood, exhaust hood, or range hood is a device containing a mechanical fan that hangs above the stove or cooktop in the kitchen. It removes airborne grease, combustion products, fumes, smoke, heat, and steam from the air by evacuation of the air and filtration.

A hood needs to be the same width as an electric cooktop and if you have gas must extend 3 inches on either side. So a 30 inch electric range needs a 30 inch wide hood. A 30 inch gas stove needs a 36 inch wide hood. As far as height above the the cook top, each hood has its own installation guide.