Condensation in AC ducts can be caused by improperly sealed openings or a lack of proper insulation around the AC duct. Condensation occurs when the outer portion of the duct work is cooled down and comes into contact with warmer air, according to Ace Plumbing.
Condensation, also known as sweating, is not always a bad thing, although there are ways to prevent it from happening. It is important that the space around the duct work be properly ventilated, especially in small spaces such as an attic or crawl space. A ventilation system allows for a consistent stream of air flow to help keep the air around the duct cool. If the ventilation system is not properly sealed at the openings, warm air is able to sneak in and cause condensation. To avoid this, simply check each opening, and verify the tightness and connection of the seal.
The AC duct needs to be properly insulated to avoid excessive amounts of condensation. Adding a vapor barrier and a layer of insulation to the duct work can help increase the temperature of the air around the air conditioning unit. If the temperature of the air going into the unit is similar to that of air near the unit, the possibility of condensation is decreased, explains Ace Plumbing.