Televised ducts under slab floor. Ducts are spiral wound galvanized ducts that are showing heavy signs of rust. The plenum under the furnace is also extremely rusted allowing rocs, sand and dirt to enter the system. The addition portion of the house in the front of the house is PVC and appears to be in good condition at this time. Suggest spin cast mortaring the galvanized ducts then spray lining the entire system with Duct Armor duct lining material.