Centrifugal fans can be used in exhaust or supply arrangement. The airflow enters the fan in one direction and leaves in different direction. Centrifugal fans can have single inlet where the airflow enters the fan from one side, or double inlet where the airflow enters the fan from two sides. They are used for HVAC applications and industrial process applications. 

There are three primary types of centrifugal fans: Forward Curved, Backward Curved fans and Radial fans.

Forward Curved centrifugal fans (a.k.a. squirrel cages) are well suited for moving large volume of airflow at low pressure (usually up to 5”wg). They are commonly used in HVAC applications. The fan blades are curved forward in the direction of rotation. Forward curved centrifugal fans are considered compact which make them suitable for limited space applications. Forward curved centrifugal fans run at relatively lower speed, which permits lighter weight construction, and lower cost fan. 

Backward Curved centrifugal fans are suitable for HVAC and clean air industrial applications. The fan blades are inclined opposite to the direction of rotation. Backward curved centrifugal fans run at higher speed than forward curved centrifugal fans which usually results in a heavier construction. Backward curved centrifugal fans have non-overloading power characteristic.

For a given duty airfoil blades impeller provide higher efficiencies than single thickness blades impeller, which makes it a good choice for energy savings. Airfoil fans are used for large HVAC applications, and for clean and dry air industrial applications too. 

Single thickness blades provides slightly lower efficiencies than the airfoil type. They are used for HVAC and clean air industrial applications. They can also handle very light dust loading in some industrial application (e.g. clean side of a dust collector).

Radial blade centrifugal fans are used primarily for material handling application, but they are also used for clean air applications. The blades are radial from the hub. In general, radial wheels have simple design rugged construction, and are easy to repair due to the material build up resistance most radial blade fan designs have. Radial blade fans are commonly used for medium to high pressure industrial applications. Radial blade fans are generally noisier and less efficient than other centrifugal fans.

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