DOI: 10.7764/RDLC.18.1.145An energy audit is a useful tool that sets out possibilities for improvement, optimization and energy saving. For the study of the thermal envelope, it is useful to use energy simulation tools that use suitably validated reference climates and simulation procedures. The results of the Unified Lider Calener Tool (HULC), and its subsequent processing of results, allow intervention priorities to be established aimed at aiding the energy manager of the building when proposing energy reform measures involving a degree of economic savings, so that the proposed investments allow a reasonable payback period. A teaching center has been chosen as a case study because presenting a tool that allows to save on energy consumption and quantify the payback terms of the investments is relevant. This paper quantifies the payback periods of the investments to be made to improve the thermal envelope of the building. To this end, the case study building was modeled and an economic analysis was carried out, which led to the conclusion that the most beneficial action is the replacement of the windows.