Exhaust ducts for clothes dryers must terminate outside the building and be equipped with which type of damper?

The correct option is the backdraft damper, which is specifically designed to prevent outdoor air from entering the exhaust duct when the dryer is not in operation. When the dryer runs, the backdraft damper opens, allowing air to flow outward, and it securely closes when the dryer stops, ensuring that cold air, pests, and other elements do not enter the ductwork and the interior of the home.

In dryer installations, avoiding the entry of external elements is critical not only for energy efficiency but also for safety and maintaining proper functioning of the appliance. The backdraft damper serves this purpose effectively, as it is constructed to create a tight seal when closed, which is essential for preventing backflow.

Other types of dampers, such as flap dampers, spring-loaded dampers, and gravity dampers, do not provide the same level of sealing and functionality needed for dryer exhaust systems. While they might offer some form of airflow control, they are not specifically designed to block backdraft air as effectively as a backdraft damper does. Thus, using a backdraft damper ensures the proper operation and safety of the dryer exhaust system.