Upblast exhaust fans direct exhaust air away from the surface they are mounted to. This configuration helps to prevent the buildup of grease or other contaminants on building surfaces. Centrifugal upblast exhaust fans feature a wheel that can overcome high static pressures and is generally quieter than axial fans. They are most commonly used as part of a kitchen exhaust system where grease or other contaminants may be present in the airstream. Axial upblast exhaust fans use a traditional propeller that can move more air volume than centrifugal fans. They are most commonly used to exhaust stale air, heat, and odors from occupied spaces.