Sometimes during summer months the supply vents of your HVAC system can sweat with condensation. The picture here shows a supply vent in Alexandria, VA that kept sweating and even caused water marks all around it on the drywall. This is caused by insufficient air sealing around the vent when it was installed. The hot humid air of the attic above hits the cold metal where it is improperly air sealed and insulated and then it hits dew point. BOOM! Sweating occurs. If you see this in your home Comfenergy can help!