Section 6.4.3/Duct and Piping Insulation
ASHRAE 90.1 Section 6.4.3 establishes minimum insulation R-values for ductwork and piping to reduce distribution energy losses.
Supply and return ductwork must be insulated to the R-values in Table 6.8.2-1 based on the duct location (exterior, unconditioned space, conditioned space) and the climate zone. Supply ducts in unconditioned spaces typically require R-6 to R-8. All duct joints and seams must be sealed per Section 6.4.4. Hydronic piping must be insulated per Table 6.8.3-1 based on the pipe size, fluid temperature range, and whether the piping is for heating or cooling. Chilled water piping also requires a vapor retarder to prevent condensation.
Why this section exists
HVAC distribution systems can lose 20-30% of their energy through uninsulated ducts and pipes, especially in unconditioned spaces. A 120-degree heating duct running through a 30-degree attic loses heat rapidly without insulation. A 45-degree chilled water pipe in a humid space sweats and drips without insulation and a vapor retarder. Distribution insulation is one of the most cost-effective energy conservation measures, often paying for itself in 1-3 years.
What plan reviewers look for
Plan reviewers check the mechanical specifications and duct details for insulation R-values and sealing requirements. They verify the R-values against Table 6.8.2-1 for the climate zone and duct location. For piping, they check the insulation thickness against Table 6.8.3-1 for the pipe size and temperature range. They look for vapor retarder requirements on chilled water piping and cold ducts.
Common violations
Related ASHRAE 90.1 requirements
Section 6.4.4 covers duct sealing requirements. Section 6.4.1 covers equipment efficiency. IECC Section C403.7 covers equivalent duct insulation requirements. Section 6.4.3.3 covers piping insulation for service hot water systems.