ICC Commercial Mechanical Practice Exam

What type of damper must be present if dryer ducts terminate outside?

1. screen

2. backdraft damper

3. fire damper

4. none of the above

The correct answer is: backdraft damper

A backdraft damper is essential when dryer ducts terminate outside to prevent outdoor air from entering the duct system when the dryer is not in use. This type of damper allows air to flow out of the dryer vent during operation but automatically closes when the dryer is turned off, ensuring that conditioned air doesn't escape and outside air doesn't enter the building. This is particularly important for energy efficiency and maintaining indoor air quality. In addition, backdraft dampers help protect against drafts that could lead to unwanted temperature fluctuations in the home. The other types of dampers mentioned do not perform the same function. Screens, while they can be installed on vent openings, do not provide an effective airtight seal. Fire dampers are designed for fire protection in ducts that pass through fire-rated walls and are not specifically intended for dryer venting applications. Therefore, the presence of a backdraft damper is critical in this scenario to ensure proper ventilation and energy efficiency.