The Irish government is implementing policies to transition Ireland to a low carbon and environmentally sustainable economy by 2050. Ireland has sectoral targets of 600,000 installed heat pumps by 2030, currently roughly 28,000 are installed. Such a high target of heat pumps will not only have a significant effect on electricity demand but also on the management and operation of the grid. In this paper we explore residential electricity demand using an innovative dataset from a field monitoring trial of deep retrofitted homes heated by an air source heat pumps (ASHPs). To assess the effect of extreme weather events on heat pump demand and the impact of large-scale adoption of heat pumps, this paper constructs the after diversity maximum demand per home. In particular we address the research questions: what is the impact of extreme weather on heat pump demand, and which statistical distributions beat model the after diversity maximum demand per home heated by an ASHP events. The software package RStudio was used to model several different distributions. Based on goodness-of-fit statistics and criteria, a Gamma distribution best models average coincident electricity demand for homes heated by ASHPs.