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E 503.4.7.1.1 Duct and Plenum Insulation
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Supply and return ducts and plenums installed as part of an HVAC air distribution system shall be thermally insulated in accordance with Table E 503.7.2.
- Factory-installed plenums, casings, or ductwork furnished as a part of HVAC equipment tested and rated in accordance with Section E 503.4 through Section E 503.4.4.1.
- Ducts or plenums located in heated spaces, semi-heated spaces, or cooled spaces.
- For runouts 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 90.1:18.104.22.168.2]