ICC Commercial Mechanical Practice Exam

What is the maximum straight length for a clothes dryer exhaust duct without angle fittings?

1. 10 feet

2. 15 feet

3. 25 feet

4. 35 feet

The correct answer is: 35 feet

The maximum straight length for a clothes dryer exhaust duct without angle fittings is 35 feet. This length is established based on the need to ensure efficient venting of the exhaust air, which can carry moisture, lint, and heat. Longer duct runs increase resistance to airflow, which can lead to longer drying times and potential hazards, such as lint buildup, that can contribute to fire risks. In residential settings, manufacturers and building codes often recommend a maximum duct length to ensure safe and effective operation. The 35-foot length is considered acceptable when there are no bends or angles, as the straight path allows for more airflow. If fittings or bends are used, the allowable length would decrease accordingly to maintain proper airflow and performance. The other choices represent lengths that might be appropriate under certain conditions, but they fall short of the maximum established length for straight ducts, which is critical for minimizing resistance and optimizing the performance of the dryer’s exhaust system.