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Attic Issues and Attic Ductwork

Updated on May 3, 2013
Insulated attic ductwork connections
Insulated attic ductwork connections | Source

Any ductwork run in an attic needs to be insulated to avoid conducting the heat or cold of the attic space into the ductwork. Uninsulated ductwork will form condensation from the variance of temperatures that exist when air from the furnace or air conditioning unit is blown through the system for distribution. The picture to the right shows a properly insulated attic ductwork distribution system. However, there are still some issues that have caused problems in this building because of energy escaping from the ductwork at connection points.

Ductwork leaking cold air from the main trunk line to the register distribution lines.
Ductwork leaking cold air from the main trunk line to the register distribution lines. | Source

This picture shows the connection from the above picture of the distribution line connection to the main trunk line. The dark area indicates excessive air leakage. There are 26 of these connections along this trunk line making these junctions a substantial source of inefficiency. Sealing these connections with closed cell spray foam would eliminate the air leakage and also prevent temperature exchange in the attic that is indicative to causing condensation issues.

Typical duct insulation for round, flexible ductwork is R-8 fiberglass insulation with a 2 mil polyethylene vapor barrier on the exterior of the fiberglass that encapsulates the entire exterior of the flexible duct. This picture shows how important it is to makes sure that every point, especially where the ductwork connections meet is insulated and air sealed.

View of the ductwork leakage and how condensation is forming on the framing of the ceiling due to excess temperature differencial.
View of the ductwork leakage and how condensation is forming on the framing of the ceiling due to excess temperature differencial. | Source

Condensation formation is not just prevalent on the ductwork. As this thermal image shows, condensation has also formed on portions of the framing and on the reflective insulation above the larger portions of leakage from the ductwork. This process can cause significant damage over time and can be easily prevented by properly sealing the leaking junction points of the ductwork.

While this seems like a worst case type of scenario, this is actually extremely common and one reason that many moisture issues are misdiagnosed as roof leaks. This is why it is important to investigate HVAC system leakage as a possible cause of water damage in a building.


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