What is the maximum air pressure allowable in an air duct system

• A. 5
• B. 10
• C. 15
• D. 20

Answer: (B)

Air duct systems are rated by static pressure—the pressure the blower must overcome to push air through the ducts. This pressure is measured in inches of water column (inches w.c.), a small, precise unit used for ductwork. The maximum allowable static pressure is set to protect duct components, prevent leaks and excessive noise, and keep airflow performance within design. In many standard practice scenarios, the upper limit used is 10 inches of water column (about 0.36 psi). Keeping the system at or below this limit helps ensure the ducts and fittings, dampers, and registers operate reliably without being overstressed or wasting energy. If pressure exceeded this level, airflow would suffer due to friction and restrictions, components could experience damage or improper seals, and the blower would have to work harder, increasing energy use.