What device must dryer exhaust ducts for clothes dryers be equipped with?

Dryer exhaust ducts for clothes dryers must be equipped with a backdraft damper. This device serves a critical function by preventing the reverse flow of air, which is important for safety and efficiency. When the dryer is operating, the backdraft damper opens to allow lint and moist air to exit the duct, but when the dryer is not in use, the damper closes to prevent outside air, pests, and environmental contaminants from entering the duct.

Using a backdraft damper is crucial because it helps to maintain the proper airflow and pressure within the dryer system, ensuring that the dryer operates effectively while also minimizing the risk of fire hazards associated with lint build-up.

The other options do not fulfill the necessary requirements for dryer exhaust ducts. A check valve, while useful in other applications, does not provide the same air-sealing benefits as a backdraft damper. A ventilation fan is not typically installed in dryer venting systems and could lead to complications or reduced performance. An exhaust hood may also play a role in directing exhaust, but it does not provide the specific protective function of preventing airflow back into the duct when the dryer is not operational. Thus, the backdraft damper is the essential device for effective dryer exhaust ducting.