Flexible air duct connections may pass through which of the following?

• A. The floor
• B. The ceiling
• C. None
• D. The non-rated wall

Answer: (C)

The key idea is maintaining fire resistance and air-tight integrity where ducts pass through building assemblies. Flexible air duct connections are not meant to serve as a passage through floors, ceilings, or non-rated walls because these barriers are designed to resist heat, smoke, and airflow for a set period. Flexible ducts are more prone to damage, leaks, and loss of fire rating if they go directly through these barriers. The proper approach is to keep flexible ducts inside conditioned spaces or route them through protected chases using rigid metal duct, and if a duct must penetrate a barrier, use a fire-rated sleeve or collar and firestop materials to maintain the barrier’s rating. Because of these protections, there isn’t a safe, code-compliant place for flexible duct connections to pass through those surfaces without meeting those requirements, so none of those options is acceptable as a simple pass-through.