Abstract: An air duct system, such as for indoor farming, includes a ventilated air duct assembly coupled to a fan, typically via an air housing. The air duct assembly has a pair of duct sections with upper and lower panels and a pair of side panels. The panels are hinged together at respective edges to form a generally rectangular shape when expanded to a use configuration. The duct sections can be collapsed to a flat storage configuration in which the upper panel and one side panel lie atop the lower panel and the other side panel. A duct junction with rectangular cross section has opposite open ends that engage respective open ends of the duct sections to secure the duct sections in fluid communication with one another in an end-to-end arrangement. One or more of the duct section panels have air outlet openings formed in them.