I have a single floor house build in the 50's. The house is on a slab and the duct work was build into the slab. I has noticed that when it rains alot we get water in our vents. This is causing multiple issues. When we run the heater or AC it gets real humid in the house and smells like meldew. I was wondering how I would go about repairing the old ducts with out busting up my foundation. I have a down force gas furnace so running new ducts in the attic is not an option either (as far a I know).