When adjusting fan performance, how is CFM related to RPM?

CFM, or cubic feet per minute, is a measure of the airflow produced by a fan, while RPM, or revolutions per minute, indicates the speed at which the fan blades rotate. The relationship between these two variables is direct; as the RPM increases, the CFM also tends to increase, assuming other factors such as fan design and blade pitch remain constant.

This direct proportionality arises because a fan’s capacity to move air is largely dependent on how fast the blades are spinning. Higher RPM means that the blades are cutting through the air more frequently, thereby increasing the volume of air being moved per minute. In practical applications, this relationship is crucial when sizing fans or conducting airflow calculations, as understanding how changes in RPM affect CFM allows HVAC professionals to optimize system performance and efficiency.

Thus, when you adjust the RPM of a fan, you directly influence the amount of air it can move, confirming that they are directly proportional to each other.