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Why is my fan not performing on the fan curve?

Any fan worth its weight is manufactured in accordance with designs that have been tested and rated to meet certain performance conditions for given speeds. A fan performance curve is then developed to give the fan owner guidelines for what air movement to expect at the supplied speed. This fan performance curve developed by the fan manufacturer indicates the expected volume, pressure, and horsepower for the indicated speed using perfect conditions – not accounting for any variables or deficiencies in your system.

So, when you measure the fan’s performance, why isn’t it producing a volume, pressure and horsepower consistent with the fan curve you’ve been provided? Some possible reasons are as follows:

  1. Incorrect fan rotation direction. While this should always be checked at installation, you would be surprised how often it is not. The fan is typically supplied with an arrow indicating correct wheel rotation. If it isn’t, you can easily determine this by looking at the fan from the drive side.
  2. There may be a system effect. Fans are tested and rated at fixed conditions when they leave the factory. Duct may have been applied incorrectly (true “system effect” – causing non-uniform airflow), devices upstream/downstream may not be accounted for, or perhaps changes to the system have occurred since initial install.
  3. The fan wheel and shaft should be inspected to determine –
    1. Correct installation
    2. Structural integrity
    3. Actual RPM

These are starting points that may lead to answering why your fan is not performing on its curve. If you still have questions – contact Indventech at 888-864-4344 or email us at sales@indventech.com.

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