Installers must duct rangehood systems out to the atmosphere and are not permitted to allow rangehoods to blow air into ceiling spaces/voids. Ducting a rangehood either through the roof or wall is required to meet compliance. If a lazy installer allows the rangehood simply to blow into a ceiling space or void this may lead to problems such as: Odours in the home Poor function leading to build up of grease Attraction of rodents Damage to rangehood motors Void of warranty  Possible void of home insurance  Fire hazard