Abstract: A system for sealing an air duct by coating the interior of the duct with a material similar to the coating used for spray-on truck bed liners. A spray device applies the liner material to the interior surface of the ducts and the spray device is held in the center of the duct by retractable sets of wheels. The spray device is removably attached to a supply hose that provides liner material to the spray device from a storage tank via a supply pump. The supply hose is first fed through the duct, the spray head is attached to the supply hose and the liner material is sprayed onto the duct as the spray head is retracted through the duct. The system can be either computer or manually controlled and can optionally employ an electrostatic unit to put opposite electrical charges on the duct and the liner material.