Anyone know what causes water stains on a ceiling around the HVAC vent? The A/C wasn’t running at the time of the inspection. The stain was dry. In the attic, there is no other explanation for the stain other than from the HVAC duct. The flex duct seemed tightly sealed to the vent. No other vents in the house exhibit the problem.
Don’t know if the photo shows it well, but here it its.