According to the ASHRAE 2001 Fundamentals Handbook [ASHRAE, 2001], an engineer should after the initial sizing, "calculate the total pressure loss for all duct sections, then resize sections to balance pressure losses at each junction." The handbook does not explain a pressure balancing procedure. However, an experienced engineer can calculate and design a duct system that satisfies duct design requirements. Regardless of the method used, it is necessary to check duct systems for pressure balancing because an unbalanced system will not perform as intended. Typically, an imbalance results from higher than expected air flow in branch duct runs. For energy, economic, and noise considerations, it is generally advisable to reduce high air flows in ductwork by making ducts smaller rather than relying on dampers or orifices.
