Like many countries globally, the private rental sector in England and Wales contains some of the lowest quality and energy inefficient properties, despite being home to some of the most vulnerable households. This article presents a new data product that classifies small areas based on the energy (in)efficiency characteristics of private rental properties. Newly available Energy Performance Certificate (EPC) data enables analysis of detailed energy and housing characteristics for 3.9 million private rentals, representing approximately 78.8% of the total sector, using k-means clustering. Demographic datasets are then used to explore wider socio-spatial inequalities and uncertainties associated with granular, but at times incomplete, EPC data. The classification can be used to evidence how inefficiency is spatially concentrated and fragmented, with a diverse range of energy and housing conditions shaping the everyday lives of tenants.