Detailed models have been developed and integrated into a TRNSYS calculation tool to evaluate the optimal storage capacity of central electric thermal storage (ETS) units for residential applications. The tool uses hourly weather data to establish the energy use profile of residential buildings under different heating system configurations and control strategies. The reliability of the system for each configuration is determined as the percentage of time the heating system meets the heating requirement of the building. The level of reliability is used to evaluate the appropriate capacity of the system. This study investigates the theoretical development and modelling of a multi-zone building equipped with a central ETS in TRNSYS. The TRNSYS simulation results are then compared and validated against experimental data obtained during the project. Furthermore, the effect of various parameters such as system configuration, charging capacity, control strategies, heat losses from the building, and electric utility time-of-use schedules are analysed. Copyright (C) 2001 John Wiley & Sons, Ltd.