What unit is commonly used to express air flow rate in HVAC systems?

In HVAC systems, the commonly used unit to express air flow rate is cubic feet per minute (CFM). This unit measures the volume of air that passes through a given point in the system per minute, making it a critical metric for assessing heating, ventilation, and air conditioning effectiveness. CFM is particularly relevant because it directly correlates to the system's performance and efficiency in distributing air throughout a space. This measurement helps engineers and technicians ensure that the air flow meets the requirements for comfort and air quality in residential and commercial buildings.

While liters per minute and liters per second are valid units for measuring flow rates in other contexts, they are not the primary measurements used in HVAC. Gallons per hour is more relevant for liquids rather than air flow and does not apply to the assessment of air movement. Thus, cubic feet per minute is the standard metric that practitioners rely on when discussing and calculating air flow in HVAC applications.