With many air-handling units on the market offering numerous pre-engineered modular components that can be arranged in virtually anyorder, the typical specifying engineer has considerable latitude when arranging those components. The designer may be confused about theoptimum component location in order of airflow. Should we use a supply fan upstream or downstream of the cooling coil? Where should Ilocate filter banks and a humidifier dispersion grid with respect to the other components? Is it safe to use a single-fan dual-duct arrangementin which a fan delivers air down two separate ducts, hot and cold? What is the proper supply air temperature for my application? These andother questions are addressed in this paper.