This paper offers a rare insight into optimal air duct design. To achieve optimum design, three requirements must be satisfied simultaneously . Fans must operate at optimum system pressure, the ratio between velocities in all sections of a duct system must be optimal, and pressure balancing must be attained by changing duct sizes, not by using balancing devices.

Today's duct design methods are expedient procedures not addressing optimization. Using an illustrative system, the cost of each traditional design is compared to optimum conditions. As the velocity ratio between duct sections departs from its optimum ratio, the system's owning and operating cost increases. This study is applicable to single-path systems, not multipath, and does not address acoustics and other constraints such as duct routing and space limitations. Further research is necessary to develop practical duct design methods taking into consideration simplicity, economics, duct routing, space, balancing, and acoustics.

Units: SI