What happens if range hood is smaller than cooktop?
The Code requires an overhead exhaust hood to be “at least as wide as the unit and shall extend over the entire unit”. (See ICC M1504) There are exceptions (i.e.: downdraft, etc.) but must be labeled for such use.
In addition, it goes on to say the exhaust duct shall extend to the exterior with a backdraft damper and cannot be plastic.
Interesting side note: Section ICC M1504 says there shall be a minimum clear distance from the cooktop to combustible material or cabinets of 24”, but Section ICC M1901 says the distance shall be a minimum of 30”. Go figure.