Until now, a small number of studies have analysed the carbon footprint (CO2 eq. emissions) of the application of Phase Change Materials (PCMs) in conventional Thermal Energy Storage (TES) systems considering different conventional fossil fuels as the source of heat. In those scarce studies, the different environmental impact categories were estimated using, on the one hand, diverse environmental methodologies and, on the other hand, different environmental evaluation methods (the midpoint and endpoint approaches). Despite the fact that several researchers have used the Life Cycle Assessment (LCA) methodology as a tool to estimate the environmental impact of TES systems, there is no unanimity in the scientific community on the environmental evaluation method to be used. As a consequence, research results cannot be easily compared. This article evaluates the introduction of a TES system (using different PCMs) to recover the waste thermal energy released in industrial processes, which can be used in other applications, thereby avoiding fossil fuel consumption by the associated equipment to produce thermal energy. Five different fossil fuels have been considered to generate the 20 case studies that were analysed using the same methodology (LCA) and evaluation method (Global Warming Potential, GWP100, a midpoint approach). The results were used to identify the best cases, considering the environmental benefits that they generate. Additionally, this research indicates that the benefits can be achieved since, in general, the amount of conventional fuels saved is sufficiently large to balance the environmental impact associated with the inclusion of PCMs in conventional TES. Nevertheless, the selection of a PCM can increase or eliminate the environmental benefits obtained.