4.1601.2 Insulating Metal Ducts

Insulating Ducts
Desired Outcome: 
Lowered thermal conductance of duct system and minimized condensation on the duct system
Selection of duct insulation material

Duct insulation on all ducts located in unconditioned spaces will be a minimum of R-8, in accordance with local code, or buried under attic insulation, whichever is greater, and have an attached vapor retarder Vapor retarder A material that slows the passage of water vapor and contains a perm rating above 1

Hot humid and warm coastal regions will not bury ducts

Decrease heat loss and condensation problems

Duct sealing

All joints, seams, and connections in ductwork shall be securely fastened and sealed with UL UL Underwriters Laboratories 181 B-M mastics (adhesives) or mastic- plus-embedded-fabric systems installed in accordance with the manufacturer's instructions before insulation is applied

Minimize duct leakage

Attachment of duct insulation

Duct insulation will be secured to the duct system using metal wire or rot-proof nylon twine

Pattern of the wire or twine will be sufficient to securely hold the duct insulation tight to the duct

Ensure a secure connection between the duct system and the duct insulation

Taping of the duct insulation

Using a tape approved by the manufacturer, all seams and connection of the duct insulation will be taped

No gaps will exist between pieces of duct insulation

Prevent gaps in the vapor barrier Vapor barrier A material that retards the passage of water vapor and contains a perm rating of less than 1 of the insulation