What is a crucial feature that must be present at the termination of dryer exhaust ducts?

A crucial feature that must be present at the termination of dryer exhaust ducts is a backdraft damper. This component serves to prevent the backflow of air into the dryer and the ductwork, which can carry lint and exhaust gases back into the living space. The backdraft damper opens when the dryer is operating, allowing hot, moist air to escape to the outside, and automatically closes when the dryer is off. This is important not only for maintaining the efficiency of the dryer but also for preserving indoor air quality and reducing the risk of fire hazards associated with lint accumulation.

The other options do not fulfill this essential role as effectively. For example, a ventilation fan is not specifically designed to prevent backflow and is generally used for boosting airflow rather than terminating a duct. A fire damper is necessary in some situations to prevent the spread of fire through ductwork, but it doesn’t address the specific issues related to the backflow of exhaust gases. A draft hood is typically used in venting systems for water heaters or furnaces to help manage draft conditions but is not relevant to the operation of dryer exhaust ducts. Thus, the presence of a backdraft damper is critical for safety and functionality.