Commercial Duct Sealing and Insulation Requirements
Section 120.4 requires all ducts, connections and building penetrations to be sealed. Exhaust air ducts, and any duct crossing a pressure boundary, are insulated to a minimum of R-6.
Sealing is not conditional
All ducts, all connections, and all building penetrations. It is a mandatory requirement rather than a prescriptive option, so it is not traded away by taking the performance path or by demonstrating compliance elsewhere.
The insulation rule and where it bites
Exhaust air ducts, and all ducts that cross a pressure boundary, are insulated to a minimum of R-6. The pressure-boundary clause is the one that catches designs: a duct running from conditioned space out through an unconditioned plenum, roof or shaft crosses a boundary even if both ends are inside the building.
"It was sealed already" is the start of a test
Where an existing duct system is documented as having been sealed previously, that is confirmed by field verification and diagnostic testing under Reference Nonresidential Appendix NA2. The documentation opens the question rather than closing it, which surprises owners who expected prior paperwork to be accepted at face value.
Why a replacement pulls the ducts in
Because altering the space-conditioning system is an alteration, and the duct system serving it comes with the equipment. A rooftop change that adds a curb adapter and new transitions has added duct that was not there before — and on an older building the existing run is usually what fails, not the new section.
What to establish before pricing a changeout
How much duct is being added or replaced, whether any of it crosses a pressure boundary, and whether the existing system has documented prior sealing. Those three answers separate a light-touch equipment swap from a project with verification attached.
Ductless removes this entirely
A ductless system has no duct requirements to satisfy and no duct verification to schedule. That is a legitimate reason to prefer one on a retrofit, and it is worth weighing at specification rather than discovering afterwards.