The use of straighteners in the inlet duct of centrifugal fans are suggested for eliminating any inlet distortion. An experimental investigation was performed to study the effect of inlet straighteners on the performance characteristics of centrifugal fans. Two types of straighteners were used, circular tubes and zigzag cross-section with different lengths. Circular tubes with different diameters have been investigated. The study was carried out on three types of fans, namely radial, backward with exit blade angles 60