Air Distribution and Ducting Flashcards

What is the purpose of a static pressure tap in a duct system?

Answer: To measure the pressure of air against the duct wall

A static pressure tap measures the pressure exerted by air against the duct wall, perpendicular to flow direction.

Which duct shape provides the most efficient airflow per unit of material used?

Answer: Round

Round ducts have the lowest surface-area-to-cross-section ratio, minimizing friction losses and material use.

A residential duct system has excessive external static pressure. What is the most likely result?

Answer: Reduced airflow and potential equipment damage

Excessive external static pressure restricts airflow, causing the blower to work harder, reducing CFM and potentially damaging the motor.

When installing flexible duct, what maximum sag per foot of run is generally acceptable?

Answer: 1/2 inch per foot

ACCA and SMACNA guidelines allow no more than 1/2 inch of sag per foot of flexible duct to prevent airflow restriction.

What term describes the pressure loss caused by air changing direction in a duct fitting?

Answer: Dynamic pressure loss

Dynamic pressure loss refers to energy lost when air changes direction or velocity through fittings such as elbows and tees.

A supply register is delivering noticeably warm air on one side and cool air on the other side. What is the most likely cause?

Answer: Poor air mixing due to stratification upstream

Temperature stratification in the duct upstream of the register can cause uneven discharge temperatures across the grille face.

What is the recommended maximum length for a flexible duct run without a support hanger?

Answer: 4 feet

Flexible duct should be supported at intervals no greater than 4 feet to prevent excessive sagging and flow restriction.