What Causes Cooling Ducts to Sweat?

Flexible insulated ducts are more efficient and prevent condensation.

Duct condensation, or duct sweat, is caused by humid conditions and improper duct insulation. Duct sweat decreases the efficiency of the air conditioning unit and the byproducts of duct sweat present a risk to personal health and structural damage. Preventing duct sweat improves air conditioning efficiency and indoor air quality.

Condensation

Condensation results when cold air in the ducts meets warmer air in the home. Rooms ventilated with exhaust fans, such as the kitchen and bathroom, have less problems with condensation. Blackout curtains can also prevent condensation from forming on windows when cooler air in the home meets the warmer air coming in from outside.

Humidity

Humidity inside the home can cause condensation in the duct work. Dehumidifiers work to remove humid air from the home. Dehumidifiers reduce the amount of energy the air conditioner uses, resulting in smaller utility bills during the summer cooling season. Using home appliances such as stoves, dish washers, and clothes dryers sparingly during the summer months reduces the amount of extra heat in the home, which means a reduced chance for condensation in the air conditioning ducts.

Insulation

Poor or non-insulated duct work causes condensation on the ducts themselves in tight spaces such as in the attic or under the home. Efficient air conditioning systems should be installed with flexible insulated ducts rather than ducts made from sheet metal. Wrapping existing sheet metal duct work in pipe insulation is less costly than replacing existing sheet metal duct work with flexible metal duct work.

Mold and Mildew

Sweaty ducts produce mold and mildew. Mold and mildew can cause structural damage such as rotting walls. Mold and mildew reduce the air quality in the home, making it difficult for people with allergies to mold and mildew and those with respiratory ailments to breathe. Mold and mildew from condensation also reduce the efficiency and life of an air conditioning filter, leading to more frequent need to change the filter.

References

• Inspectapedia: Duct Work Ice
• HGTV Pro: Preventing Condensation on Ductwork