I have all of my ducts and furnace in a "damp" crawl space. To prevent
moisture from coming into the house via the HVAC system I want to seal my
ducts as much as possible and would like some advice on the best way to do
this. I did have someone seal all of my return ducts with mastic and was
wondering if it made sense to do the same with the supply ducts. Is there a
better way, etc?

Any advice is appreciated.

George

PS.. BTW.. I did put down 6 mil plastic on the floor of the crawl space to
help bring down the moisture it the area.. I also plan on putting a
dehumidifier down there with the goal of drying the area somewhat.