Airflow Unit Conversion
Enter the air velocity or volume airflow and the duct area, then select the appropriate units.
Clicking the calculate button without input will load the example below.
- Select the appropriate DC fan to supply 400 LFM (2 m/s) airflow into a 4 inch (102 mm) diameter circular duct with a pressure drop of 0.1 inches of water (25 Pa).
- Using the airflow calculator above, type the airflow value of 400 and select LFM as the units. Next type the circular duct dimensions of r = 2 in. After pressing the Calculate Airflow button, read the CFM requirement of 34.91 CFM in the volume airflow units column.
- This value coupled with the pressure drop of 0.1 inches of water (25 Pa) now allows the use of standard fan curves. For example, click the following link to select a 12 volt DC fan, which meets the requirement: 12 DC Fan.
- Notice that the free air delivery of fans is the airflow delivered with no resistance. The fourth fan listed, Flight II 120 – FT12B3, would deliver 37.8 CFM into the duct and 90 CFM if no resistance was presented.