What is NOT permitted for flexible air connectors?

Flexible air connectors are designed to facilitate the movement of air between duct systems and individual units or through various sections of a building. However, certain restrictions are in place regarding their installation to ensure safety and maintain the integrity of the HVAC system.

The prohibition against passing flexible air connectors through walls, floors, or ceilings is primarily for fire safety and to avoid mechanical damage. Suitable materials and construction practices must be utilized in these locations to maintain structural integrity and prevent fire spread. Allowing flexible connectors to traverse these barriers could create vulnerabilities within the building's fire-rated assemblies, leading to potential safety hazards.

Hence, since none of the options provided allow for the use of flexible air connectors in those contexts, it's accurate to state that all mentioned scenarios are not permitted. This reinforces the importance of adhering to building codes and safety regulations when planning and constructing air distribution systems.