ICC Commercial Mechanical Practice Exam

What is required for dryer exhaust ducts for clothes dryers that terminate outside of a building?

1. screen with not less than 1/4 inch mesh

2. backdraft damper and screen

3. backdraft damper

4. none of these

The correct answer is: backdraft damper

The requirement for dryer exhaust ducts that terminate outside of a building is primarily to ensure safe and efficient operation of the dryer while minimizing the risks associated with fire and the entry of pests into the duct system. A backdraft damper is specifically designed to prevent outside air from entering the duct when the dryer is not in use, thus maintaining the efficiency of the exhaust system. When exhaust systems lack a proper damper, conditioned air from inside the building can escape, which undermines energy efficiency and can lead to higher heating or cooling costs. Additionally, without a damper, there is also a risk of pests entering the duct and potentially creating blockages or nests. While some options mention screens or other devices, they may not necessarily provide the level of protection needed against backdrafts as effectively as a dedicated backdraft damper. The damper alone can serve the primary function of preventing backflow while allowing exhaust to exit when the dryer is operating, making it a critical component for safe and efficient dryer venting.