Hydration transitions of salts involve enthalpy changes that make salt hydrations interesting candidates for long term stable heat storage. The potential and limitation of this class of materials is related to parameters like the energy density, the pressure-temperature lines of the phase transitions and kinetic barriers of the solid-solid transitions. Since is there is a huge variety of compounds available, screening the right candidates for heat storage applications is an important issue. In this lecture a statistical thermodynamical framework will be discussed that enables a quick evaluation of the potential of salt hydrates. It will be shown what salt hydrates are the most suitable candidates for the application.