In the last decade, low carbon technologies for reducing the dependency on fossil fuels have been attracting attention. Domestic heating is one of the prior areas needing advanced sustainable technologies to reduce global energy demand. Population growth and the increasing comfort demand in dwellings have caused a sharp rise of fossil fuel consumption in the last 50 years. On the other hand solar energy is counted as one of the promising renewable sources and has a great potential for thermal energy generation. However the mismatch of solar energy availability and building heat loads in winter conditions constitutes a drawback needed to be overcome for increasing solar share in space heating applications. Thermochemical heat storage system is a promising alternative for long term – seasonal storage of solar energy without any heat loss which seems difficult with sensible or latent heat storage systems. In this study the cyclic behaviour and thermal performance of nano-composite matrix “Vermiculite-CaCl2” is experimentally investigated. A novel open thermochemical reactor consisting of meshed tube diffusers was developed for conducting the experiments. Results showed that “Vermiculite-CaCl2” has a good cyclic behaviour. Additionally it is found that 0, 01 m3 of Vermiculite-CaCl2 can provide an average temperature lifting of air, ΔT~20 °C over 180 minutes corresponding to ~1 kWh heat output. The results suggested a linear correlation between thermal performance and moisture uptake. Concordantly an “operating line” showing the instantaneous ΔT – Δw relation for certain inlet air conditions is numerically generated. Experimental results were used to validate the model and it was found that a numerically achieved operating line is in close approximation with the test results. Determining operating lines will be useful for effective design and control of thermochemical heat storage systems.