Thermal energy storage has been identified as a key component of decentralised energy systems. However in family houses where the place may be restricted or expensive there is not always sufficient place when thermal storage has to be installed. Thus, thermochemical heat storage appears to be relevant towards these problems because they provide negligible heat loss and high energy density. This paper investigates an innovative thermochemical system dedicated to household for long term storage purposes. Thermochemical materials particularly salt hydrates have a significant potential for use in thermal energy storage systems. Existing Domestic Hot water Tank (DHWT) is enclosed within a new adsorbent thermochemical reaction jacket containing the new high energy density composite of salt impregnated within a host matrix Vermiculite (expanded). The composite utilizes reversible reaction of salt and moisture vapour to produce heat. The salt used in this work is Calcium chloride (CaCl2). Thermal regulation controls the (DHWT) water flow to ensure adequate temperatures are maintained during reversible hydration/dehydration cycle. Desorption of moisture from the composite is referred to as the ‘charging cycle’, and when required, the composite may be discharged by passing moisture laden air, received from the extracted interior moisture of the house (cooking, showering etc.,) through adsorbent jacket. The originality of this work lies in the fact that the thermal reaction (chemical and sorption) of the composite can thus be utilised to provide direct air heating to the hot water in the (DHWT). A new prototype has been built and tested in laboratory under conditions representative of UK winter. Results exhibit an average output temperature of 40°C is experimentally obtained, however still insufficient as expected because of a low heat transfer at the interface between the reactive layer and the water tank wall. Though promising conclusions have been obtained regarding the feasibility and performance of such a storage processes.