Reducing electricity consumption is of great importance by improving the operation performance of the heating systems based on solar-assisted air source heat pumps for domestic heating. The set hot-water-supply temperature of the heating system affect both the system operation performance and the indoor thermal comfort condition. The effect of low temperature heating on the system operation performance is investigated to figure out the way to significantly save electricity. A single-family house is chosen as the reference building and the heating system is modelled and simulated under the weather conditions in the locations of London, Aughton and Aberdeen in the UK over a year. The set hot-water-supply temperatures are taken to be 40 oC, 45 oC, 50 oC and 55 oC. For the heating systems, with the decrease in set hot-water-supply temperature from 55 oC to 40 oC, the yearly seasonal performance factor increases by 16.7%, 19.1% and 15.4% in London, Aughton and Aberdeen, respectively. Consequently, the yearly total electricity consumption decreases by 19.1%, 14.9% and 13.3% in London, Aughton and Aberdeen, respectively. The results show that low temperature heating enables significant reduction in electricity consumption of such heating systems.