Selection Between Forward Curve & Backward Curve in Line Fans

If dust or other sticky stuff is present, radial vanes will shed it the best. If actual conditions differ from design estimates, forward curved vanes can overload the motor. This is less of a concern with backward curved vanes, but I think they are less efficient than a well matched forward curve selection. (It has been a while since I consulted a fan book, so other input may be better.) Some fan catalogs feature an engineering section that may give good guidelines.

Only backward curved fans are preferable unless high pressure rise is needed. Also efficiency of backward curved fans are better. you should give more details like flow rate, temp, pressure etc. for better comments.