A duct system for a refrigerator appliance is provided. A fresh food supply duct provides fluid communication between an evaporator chamber and a fresh food chamber. A convertible chamber supply and return duct each provide fluid communication between the evaporator chamber and a convertible chamber. A dual damper is operably coupled to the convertible chamber supply and return duct for selectively and simultaneously opening or closing the convertible chamber supply duct and the convertible chamber return duct.