Supply and return ducts and plenums installed as part of an HVAC air distribution system shall be thermally insulated in accordance with Table E503.7.2.
- Factory-installed plenums, casings, or ductwork furnished as a part of HVAC equipment tested and rated in accordance with Section E503.4 through Section E503.4.4.1.
- Ducts or plenums located in heated spaces, semi-heated spaces, or cooled spaces.
- For run outs less than 10 feet (3048 mm) in length to air terminals or air outlets, the rated R-value of insulation shall not be required to exceed R-3.5.
- Backs of air outlets and outlet plenums exposed to unconditioned or indirectly conditioned spaces with face areas exceeding 5 square feet (0.5 m2) shall not be required to exceed R-2; those not exceeding 5 square feet (0.5 m2) shall not be required to be insulated. [ASHRAE 90.1:184.108.40.206.2]