Skip Navigation to main content U.S. Department of Energy U.S. Department of Energy Energy Efficiency and Renewable Energy
Bringing you a prosperous future where energy is clean, abundant, reliable, and affordable EERE Home
Federal Energy Management Program
 
About the ProgramProgram AreasInformation ResourcesFinancing MechanismsTechnologiesServicesHome
Operations and Maintenance Home Page
Technologies Air Compressors Boilers Building Automation Systems Chillers Cooling Towers Fans Types Key Components Diagnostic Tools Safety Case Studies Maintenance References Lighting Motors Pumps Steam Traps
Advanced Metering
Strategies
Resources
Contacts

Types of Fans

The two general types of fans are axial-flow and centrifugal. With axial-flow fans, the air passes through the fan parallel to the drive shaft. With centrifugal fans, the air makes a right angle turn from the fan inlet to outlet.

Axial Fans

Picture of a propeller fan. Illustration created for web by Technologists Inc., for use with FEMP O&M Best Practices, as a model. - Click to enlarge.

Propeller fan—Click image to enlarge and view reference.

Propeller fans—The basic design of propeller fans enhances maintenance to remove dust and dirt accumulations. The fan normally consists of a "flat" frame or housing for mounting, a propeller-shaped blade, and a drive motor. It may be direct drive with the wheel mounted on the motor shaft or belt driven with the wheel mounted on its own shaft and bearings.

Picture of a tube-axial fan. Illustration recreated for web by Technologists Inc. using graphic supplied by The Institute of Agriculture and Natural Resources, University of Nebraska to PNL, for use with FEMP O&M Best Practices, as a model. - Click to enlarge.

Tube-axial fan—Click image to enlarge and view reference.

Tube-axial fans—A tube-axial fan consists of a tube-shaped housing, a propeller-shaped blade, and a drive motor. Vane-axial fans are a variation of tube-axial fans, and are similar in design and application. The major difference is that air straightening vanes are added either in front of or behind the blades. This results in a slightly more efficient fan, capable of somewhat greater static pressures and airflow rates.

Centrifugal Fans

Picture of a centrifugal fan. Illustration recreated for web by Technologists Inc. using graphic supplied by The Institute of Agriculture and Natural Resources, University of Nebraska to PNL, for use with FEMP O&M Best Practices, as a model. - Click to enlarge.

Centrifugal fan—Click image to enlarge and view reference.

Often called "squirrel cage" fans, centrifugal fans have an entirely different design. These fans operate on the principle of "throwing" air away from the blade tips. The blades can be forward curved, straight, or backward curved. Centrifugal fans with backward curved blades are generally more efficient than the other two blade configurations. This design is most often used for aeration applications where high airflow rates and high static pressures are required. Centrifugal fans with forward curved blades have somewhat lower static pressure capabilities but tend to be quieter than the other blade designs. Furnace fans typically use a forward curved blade. An advantage of the straight blade design is that with proper design it can be used to handle dirty air or convey materials.