Define 'static pressure' in a central HVAC duct system.

Define 'static pressure' in a central HVAC duct system.

• A. The temperature drop across a coil
• B. The resistance to airflow within the duct system, measured in inches of water column, affecting fan performance
• C. The velocity of air in the duct
• D. The rate of air volume flow in CFM

Answer: (B)

Static pressure is the resistance the moving air encounters as it travels through the duct system. It’s the amount of pressure the blower has to generate to push air through ducts, filters, coils, fittings, and other restrictions. It’s measured in inches of water column and represents potential pressure in the duct, not the speed of the air. This is why static pressure directly affects fan performance: higher resistance means the fan must work harder and airflow can drop, while lower resistance makes it easier for air to move but isn’t about how fast the air is traveling. In practice, technicians measure static pressure with taps and a manometer to ensure the fan and duct design deliver the intended airflow.

Static pressure is the resistance the moving air encounters as it travels through the duct system. It’s the amount of pressure the blower has to generate to push air through ducts, filters, coils, fittings, and other restrictions. It’s measured in inches of water column and represents potential pressure in the duct, not the speed of the air. This is why static pressure directly affects fan performance: higher resistance means the fan must work harder and airflow can drop, while lower resistance makes it easier for air to move but isn’t about how fast the air is traveling. In practice, technicians measure static pressure with taps and a manometer to ensure the fan and duct design deliver the intended airflow.