What must all general exhaust ducts include?

In mechanical ventilation systems, particularly those involving general exhaust ducts, including a backdraft damper is crucial for ensuring correct functionality and safety. A backdraft damper serves to prevent the reverse flow of air when the exhaust fan is off or when there is a pressure imbalance. This helps to maintain the intended airflow direction within the ductwork and prevents outside air, pollutants, and potential contaminants from re-entering the building. Additionally, it protects the system components and improves energy efficiency, as it reduces the loss of conditioned air.

In contrast to the backdraft damper, the other options have specific roles that may not apply universally to all general exhaust ducts. For instance, a fire dampening system is more relevant for ducts that carry flammable materials or are in fire-sensitive environments. A vent hood is specialized equipment typically associated with kitchens or areas requiring localized exhaust rather than a requirement for all general exhaust systems. Finally, while filtration systems are essential for certain types of exhaust, implementing them in all general exhaust ducts is not standard, as the primary function of these ducts may not necessitate filtering contaminants to the same extent.