Residential Building Inspector B1Building Planning and Life SafetyHard
A residential building inspector is performing a final inspection of a newly constructed single-family dwelling. The dwelling includes a permanently installed clothes dryer. What is the maximum length permitted for a 4-inch (102 mm) diameter smooth-wall flexible metal duct for a clothes dryer exhaust?
- A25 feet (7620 mm)
- B8 feet (2438 mm)
- C14 feet (4267 mm)
- D20 feet (6096 mm)
Show answer & explanationAnswer & explanation
Correct answer: B. 8 feet (2438 mm)
Clothes dryer exhaust ducts have strict length limitations to ensure proper airflow and prevent lint buildup, which can be a fire hazard. Flexible ducting has even tighter restrictions.
Why the other options are wrong
- A. This length significantly exceeds the maximum for any type of dryer duct.
- C. This length is typically the maximum for rigid metal ducts with no bends.
- D. This length exceeds the maximum for any type of dryer duct.
Dryer Exhaust Duct Length (Flexible)
The maximum length of flexible metal ducting for clothes dryer exhaust is limited to prevent excessive back pressure and lint accumulation.
- Flexible ducts have shorter limits than rigid ducts.
- Each bend reduces the effective straight duct length.
- Ensures efficient drying and reduces fire risk.
Memory trick: Flexible duct, eight feet's the rule, no longer, or you're a fool!