What is NOT permitted in a corridor when used for returning air?

In a corridor used for returning air, it is crucial to maintain a safe and efficient environment for both occupants and systems. Exhaust fans introduce air from the corridor into the exhaust system, which can create negative pressure and disrupt the airflow dynamics of the HVAC system. This disruption may result in undesirable conditions, such as backdrafting of combustion appliances or creating areas of stagnant air. Additionally, placing exhaust fans in a return air corridor complicates the management of air quality and ventilation, possibly leading to the circulation of contaminated air back into the occupied spaces.

In contrast, other options like HVAC ducting, outdoor air, and heat recovery ventilators can generally facilitate proper airflow and energy efficiency when appropriately installed. HVAC ducting is necessary for distributing conditioned air, outdoor air is essential for maintaining indoor air quality, and heat recovery ventilators can enhance energy efficiency by recovering heat from exhaust air while allowing fresh outdoor air to enter without creating an imbalance. Therefore, exhaust fans are specifically not permitted in this context due to their potential negative impact on airflow and air quality in return air corridors.