Fans are normally the work horse of air handling systems--a dependable, efficient method of moving air. Unfortunately, many fan installations are not as satisfactory as they should be, because fan performance in the field is quite different than fan performance in the testing laboratory. Normally, this discrepancy is due to imperfect inlet and/or outlet duct work conditions.

This paper summarizes various inlet and outlet duct fittings for axial and centrifugal fans and offers pressure-loss values for these fittings. These values may then be added to the normal pressure calculations to determine a better estimate of the field requirements for the fan.

These pressure-loss factors are the best estimate of a number of investigators and may be adjusted by the designer for his actual application.