The use of electronically commutated motors (ECMs)and modulation control valves in hydronic fan coil units (FCUs) enable moreprecise load tracking operation by varying both airflow and water flow.Considering the fact that HVAC equipment are rarely operating at their fullload conditions for an extended period of time, the modulation control thatvaries fan and pump speeds to meet the thermal load has great potential forenergy savings compared with conventional on-off control that cycles airflowand water flow. The goal of ASHRAE RP-1741 is to benchmark the energy savingsof modulation control relative to the conventional on-off control for hydronicFCUs. As a first step, 47 FCUs from three manufacturers were experimentallyevaluated over a range of air and water flow and thermal conditions using apsychrometric testing facility.