Hi all, I searched the forums but could not find a suitable answer. Here is my problem: I recently finished my basement (house is 7 years old) and discovered some stains on the new suspended ceiling tiles. It is being caused by a hvac duct that is sweating. This has not happened before finishing the basement and the basement is very dry.

It has been very hot and humid here in Maryland recently. My theory as to why the duct is sweating is that particular duct passes directly over the main return duct for the hvac system. Several returns from my upstairs bedrooms pass right in this area causing it to be slightly warmer and enough of a temperature gradient to cause the condensation.

My first course of action was to remove several ceiling tiles to get ventilation and blow a small fan up toward the area to try to normalize the temp. It continued to sweat, so I popped more ceiling tiles out and insulation with fiberglass all around the main return and then insulated the 6" duct that has been sweating with a 5 foot fiberglass wrap.

It is still sweating, matter of fact it is sweating farther down the duct as well. Does anyone have a solution/suggestion before I call professional in? BTW, I did add 1 supply duct in the main run and 1 cold air return in the basement. A friend of a friend does hvac work for a living and he said that would be fine to do.

Thanks in advance