Any variable air volume system duct upstream of the VAV boxes shall meet seal class ______.

Any variable air volume system duct upstream of the VAV boxes shall meet seal class ______.

• A. Class D
• B. Class A
• C. Class C
• D. Class B

Answer: (C)

Duct sealing classes specify how much air can leak from a duct when it’s tested at a standard pressure. For a variable air volume system, the main supply duct that runs upstream of the VAV boxes carries the air distributed to multiple zones, so leaks here directly affect the actual airflow reaching the boxes and the system’s energy efficiency. Requiring the upstream ductwork to meet a mid-range seal class, Class C, provides a practical balance: it limits leakage enough to maintain accurate air delivery and energy performance without the higher cost of the strictest class. The other options would be either unnecessarily tight (more cost with little extra benefit in most installations) or too lenient for reliable operation.

Duct sealing classes specify how much air can leak from a duct when it’s tested at a standard pressure. For a variable air volume system, the main supply duct that runs upstream of the VAV boxes carries the air distributed to multiple zones, so leaks here directly affect the actual airflow reaching the boxes and the system’s energy efficiency. Requiring the upstream ductwork to meet a mid-range seal class, Class C, provides a practical balance: it limits leakage enough to maintain accurate air delivery and energy performance without the higher cost of the strictest class. The other options would be either unnecessarily tight (more cost with little extra benefit in most installations) or too lenient for reliable operation.