The adoption of Air-to-Water Heat Pumps (AWHPs) is a promising retrofit strategy for reducing heating energy consumption and decarbonizing domestic heating in temperate climates. In this paper, an AWHP with supplementary electric heating has been employed as a retrofit heating strategy for 756 house archetypes, which have been selected to represent the housing stock of the North-East region of England. The objective of this study is to investigate the effectiveness of the AWHP system in terms of both the system’s energy use and the extent to which the system has sufficient capacity to meet the space heating demand of the buildings. As a result of the study, the paper reveals that only 482 house archetypes (with their current level of therma...