Understanding Fan Curves

What is a Fan Curve?
It is a characteristics curve, which shows the relationship between static pressure and the air flow rate of the fan. The fan manufacturers perform actual test to find out the static pressure value of the fan for the different air flow rates to plot the fan curve.

Please note from the fan curve that, as the flow rate increases the static pressure decreases, means at higher flow rate the fan will be able to withstand lower system resistance (or back pressure).

How to Select a Fan

  • After you posses the fan curve from the supplier, you have to know or create one more curve that is system curve.
  • The intersection point of the fan curve and the system curve will give you the operating point of the fan or you can tell your fan supplier what is the static pressure and flow rate you are looking for.
  • The fan supplier will then select a suitable sized motor to the fan.


The article has explained the fan curves basics, but drawing correct system curve is not a easy task and selecting the fan’s operating point depends largely on preparing correct system curve. I will write something next on how to draw a system curve.

Image Courtesy

Bureau of Energy Efficiency


Shibashis Ghosh

Hi, I am Shibashis, a blogger by passion and engineer by profession. I have written most of the articles for mechGuru.com. For more than a decades i am closely associated with the engineering design/manufacturing simulation technologies.
Disclaimer: I work for Altair. mechGuru.com is my personal blog. Although i have tried to put my neutral opinion while writing about different competitor's technologies, still i would like you to read the articles by keeping my background in mind.

3 Replies to “Understanding Fan Curves”

  1. Dear Suve,
    Thank you for your great article.I am not sure to well understanding the differences between fan curve and system curve.Why in system curve the pressure increases when the flow increases.On the other hand,in fan curve,as the flow increases,the pressure decreases.
    Looking forward to hearing from you at the earliest.
    Best Regards

    1. Well, let’s start with the fan, The input power for a fan can roughly be calculated using the following equation: input Power (KW) =(flow rate X pressure)/fan efficiency. You see for a fixed amount of input power for a fan, the pressure will decrease with the increase of flow rate. Now, for a system (lets say a air tight compartment), as flow of air increases i.e., the more and more air are pushed inside the compartment, the pressure will keep increasing. Hope it clears.

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