A new dwelling has 6-inch-diameter round supply and return ducts for its forced-air heating and cooling system running through an unconditioned attic, outside the building thermal envelope. The ducts are not buried in ceiling insulation and do not qualify as being inside conditioned space. When checking the duct insulation alone under the 2024 IECC residential provision for ductwork outside conditioned space, what minimum insulation R-value applies to these ducts?
- R-8 for both supply and return ducts
- BR-6 for both supply and return ducts
- CR-8 for supply ducts and R-3 for return ducts
- DR-13 for both supply and return ducts
Where to look it up
https://dos.ny.gov/nys-energy-conservation-construction-code-noa-7242025
Why A is correct
Both ducts require at least R-8: the outside-conditioned-space rule applies the same diameter threshold to supply and return ductwork. These 6-inch ducts are in the 3-inch-and-larger group. Ductwork smaller than 3 inches instead has an R-6 minimum under this provision; there is no R-3 return-duct allowance here. This checks duct insulation only, not every energy or mechanical requirement. Source: 2024 IECC residential R403.3.3, reproduced without a New York modification in the official 2025 ECCCNYS, printed page 259 (PDF page 262). The separate New York duct-location amendment is not applied to this model-code question. https://dos.ny.gov/nys-energy-conservation-construction-code-noa-7242025