Abstract This study is concerned with the development of a heat pump incorporating thermochemical energy storage. The heat pump was designed to utilise the cheap ‘Economy 7’ electric tariff with ambient air as the heat source. A domestic-sized heat pump, featuring two-stage compression and incorporating a NH 3/liquidised CaCl 2 system, was built and tested. The average value of the coefficient of performance was 2·8. Experimental tests of liquidised absorbent systems are described together with an analysis of the results.