Under what condition is equipment and devices permitted in ducts or plenum chambers?

Equipment and devices are permitted in ducts or plenum chambers primarily if they are necessary for their direct action. This means that if a piece of equipment needs to be located within these spaces to fulfill its intended function—such as motors or fans that help in air movement—then it is allowed.

The reasoning behind this regulation ensures that any installed equipment within ducts or plenum chambers is essential and justified, thereby minimizing interference with airflow, reducing fire hazards, and maintaining the integrity of the HVAC system.

In contrast, options involving sensing air quality or assessing air temperature may require additional considerations or regulations, especially if they are not essential for the system’s direct operation. Therefore, while those functions are important for system monitoring and overall efficiency, they do not universally permit the presence of equipment in ducts or plenum chambers without specific context or justification as outlined in the regulations.