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Inlet Box

A rectangular box designed to turn the air through 90 degrees into the fan inlet.

The box should have the correct proportions and size otherwise the fan performance will suffer. The volume flow is particularly affected by a poor design of inlet box (and poor inlet duct configuration).

A large aspect ratio (width/depth) is recommended with a tapered back to give good fan performance.

Inlet boxes enable double width fans to have bearings mounted outside of the gas stream and is particularly useful for large fans in dirty applications - see screen shot.

An inlet box can also be used with single width fans to provide a centre supported impeller design for the same reason. Centre supported impellers tend to run more smoothly in dirty applications but can give expansion problems in high temperature applications.