Jim Rooney, a construction expert, says that condensation on the outside of cold duct work is the most common cause of dripping water. Hot, humid air surrounds the thin metal duct work used under houses and causes any moisture in the air to condense. The same process causes condensation to gather on the outside of a cold glass of water in a hot room. According to Rooney, keep the air conditioning set at a specific temperature during the warm months of the year to reduce condensation. This works to keep the crawlspace or basement where the duct is located cool enough to prevent condensation.
Inadequate insulation on the duct work underneath your home can cause water to gather and lead to rotten wood or mold. Bob Vila, a well-known home improvement expert, explains that poorly insulated duct work also raises the cost of cooling a home because the air warms quickly as it travels through uninsulated duct work. Flexible, plastic, pre-insulated duct work can be installed to prevent water drips, or traditional fiberglass insulation can be wrapped around the ducts.
Although duct work on a home rarely runs through both the attic and basement or crawl space of a home, if it does, dripping water could be coming from a leak in the ceiling. The experts at Inspectapedia say that gaps or openings in the duct work located on the roof or in the attic of a building can let water into the ducts, which will then leak out at the lowest point of the system. Water entering the ducts in the attic would also indicate the presence of a leaking ceiling.