Hi- I have run across condensation in a home furnace cold air intake duct (only in the winter). The duct ties directly into the return air duct and routes to the exterior wall just above grade. The duct is insulated well. I found the the homeowner has been running the fan continuously which may have been the problem. either way I have to replace the entire duct to from exterior wall to cold air return. Not sure what I will do will be any better than the privious insulated duct. It was also well insulated at the exterior wall so im stumped. The basement is very dry- driest i have ever seen so it is not a humidity issue either. Anybody run into this??