Ebm-papst centrifugal fans are available with forward or rear curved blades. Low noise centrifugal fans with forward curved blades are also provided with a roll cover. Centrifugal fans with curved blades are designed as free fans and do not require rolls. For centrifugal fans with external rotor motors, the engine is placed in the rotor, resulting in optimum engine cooling as well as a particularly compact design. The entire product line is available in both AC technology and GreenTech EC.