A traditional mass and energy balance component approach was used to characterize the performance of fixed-airflow series fan-powered terminal units for applications in building simulation programs. The approach included developing relevant energy and mass balance equations for the components in a fan-powered terminal unit--heating coil, fan/motor combination, and mixer. Fan motors that included permanent-split-capacitor motors controlled by silicon-controlled rectifiers or electronically commutated motors were included in the model development.The paper demonstrates how to incorporate the fan/motor combination performance models for both permanent-split-capacitor and electronically commutated motors into the mass and energy balance approach. The fan models were developed from performance data that were provided by multiple fan-powered terminal unit manufacturers. The fan/motor performance data included a fan airflow range from 250 to 3500ft³/min (0.118to1.65m³/s) and a motor size range from 0.333 to 1 hp (248.6 to 745.7 W).