Semi-empirical models were developed for fan airflow output, fan power consumption, and primary airflow for series fan-powered variable-air-volume terminal units with electronically commutated motors. Eight series terminal units with either 8 in. (203 mm) or 12 in. (304 mm) primary inlets from three terminal unit manufacturers and two motor manufacturers were evaluated. Fan power and airflow data were collected at a downstream static pressure of 0.25 in. w.g. (62.3 Pa). Upstream static (primary air) pressures were varied from 0.0 to 2.0 in. w.g. (0 to 498 Pa). Data were collected at four primary inlet damper positions and at four fan motor settings. Model variables included primary air inlet damper position, fan motor input setting, the air inlet differential sensor pressure, and the upstream (primary air) and downstream (supply air) static pressures. All of the resulting fan power and airflow models had R2 values greater than 0.895. The models for the fan airflow output and fan power had R2 values greater than 0.968. The models developed in this paper can be used in HVAC simulation programs to estimate the energy use and potential savings of series fan-powered terminal units with electronically commutated motors.