The speed of air through a duct is measured in _____?

The speed of air through a duct is measured in feet per minute because this unit specifically conveys how far air travels within a given timeframe. In HVAC systems, understanding air velocity is crucial for calculating airflow rates and ensuring adequate ventilation. Feet per minute quantifies the linear velocity of air moving through the ductwork, which is important for assessing system performance and efficiency.

The other options represent different measurements not related to air velocity in duct systems. Gallons per hour pertains to fluid flow rates, inches of water typically measures pressure differentials in the system, and square feet is a unit of area that does not apply to the velocity of air in ducts. Each measurement serves its purpose, but when assessing the speed of moving air specifically, feet per minute is the standard unit of measure.