This research aims to diagnose the energy performance of buildings in València and identify areas where energy efficiency can be improved. The energy performance results of all 129,487 EPCs in the city were mapped and compared to socioeconomic variables to gain insights into the reasons behind the results. The study reveals that the city's building stock has poor energy performance, attributed to the lack of building standards during the city's expansion in the 1960s and 1970s. The worst energy performances are observed in the peripheral districts, particularly in the city's northern half, where low-income and low-renting rates are common, resulting in reduced investment capacity for individuals to retrofit their homes. To promote quick dissemination of measures to retrofit households, they must be adequate, economical, and replicable, avoiding social, administrative, and economic barriers. The study highlights the importance of EPCs as an objective tool to diagnose the energy efficiency of a city's building stock. Policymakers can use the findings to identify areas that require improvements and evaluate the appropriate actions to improve the building stock's energy performance. This study presents significant potential to reduce buildings’ energy demand and achieve climate goals through EPCs.