What is the formula to calculate duct size in HVAC systems?

The formula to calculate duct size in HVAC systems is derived from the basic relationship between airflow (measured in cubic feet per minute or CFM), duct velocity (measured in feet per minute or FPM), and duct cross-sectional area. The correct formula states that duct size can be calculated by dividing the airflow (CFM) by the duct velocity (FPM).

When considering airflow in an HVAC system, it's crucial to ensure that the ducts can transport the required volume of air efficiently, which involves establishing an appropriate velocity that the air will travel through the duct. By using the formula where duct size is equal to CFM divided by velocity, you can determine the necessary cross-sectional area needed for the duct to maintain an efficient and effective airflow that meets the system's requirements.

The formula's application is practical; it allows technicians and engineers to design ductwork that can effectively handle the specified airflow without causing excessive pressure drop or noise, factors that can negatively impact system performance.

The incorrect options either misapply arithmetic operations or present relationships that do not logically correspond to how duct sizing is determined in HVAC systems.