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Thermochemical materials K₂CO₃, MgCl₂ and Na₂S have been investigated in depth on energy density, power output and chemical stability in view of domestic heat storage application, presenting a critical assessment of potential chemical side reactions in an open and closed reactor concept. These materials were selected based on a recent review on all possible salt hydrates, within the frame of a thermochemical heat battery and considering recent advances in heat storage application. Judged by gravimetric and calorimetric experiments in operating conditions and worst-case-scenario conditions, K₂CO₃ is recommended for both an open and closed system heat battery. The compound is chemically robust with a material level energy density of 1.28 GJ/m³ in an open system and 0.95 GJ/m³ in a closed system, yielding a power output of 283–675 kW/m³. Na₂S and MgCl₂ on the other hand are chemically …