No, kitchen exhaust fans do not have to be vented outside, but they should be. The fan pulls air from the kitchen and exhausts it outdoors. This helps remove cooking vapors and odors from the kitchen. Without a fan, these vapors and odors will linger in the kitchen, and can cause respiratory problems for people in the home. In addition, a fan helps cool the kitchen, which can make it more comfortable to cook in summer. If you don't have an outdoor exhaust fan, you can vent the fan into the attic or basement. Be sure to route the ductwork so that it does not come into contact with any flames or heat sources.

Kitchen exhaust fans do not have to be vented outside, but they should be vented to the outdoors if possible. If the fan is not vented to the outdoors, it should be vented to a tightly sealed room such as a garage.