This paper presents the design and the characterisation of a high powered energy dense zeolite thermal heat storage system using water vapour sorbate. The specification requirements of the system are to supply a heating power of 2 kW during 2 h in order to shave the electricity peak loads in a house. The open reactor has been designed, built and instrumented with temperature sensors, chilled mirror hygrometer and airflow meter. Several tests have been carried out both during hydration - heat release - and dehydration - heat storage. Tests have also been carried out for different flow rates, relative humidity and temperatures of hydration. The results show that the reactor can supply a constant power of 2.25 kW during more than two hours, namely 27.5 W kg(-1) of material. (C) 2015 Elsevier Ltd. All rights reserved.