Dynamic thermal simulation is attracting the interest of designers thanks to the availability of numerical codes. However, one of the main problems facing the potential users is hourly-weather data availability. In Italy, the main source for the data is drawn upon the IGDG database. It is provided by the EnergyPlus weather site and the related measurements were collected between 1951 and 1970. A new set of files, gathered between 1989 and 2014, has recently become available. Nevertheless, it needs additional work to be directly implemented in energy simulation codes, which can lead users to download and apply the already available IGDG database files. In order to evaluate the ensuing effects, 52 Italian weather file locations were selected, and two simulations were carried out on seven multifamily-house models considering the difference between the results obtained using the old and new weather data. Since the locations of the two databases do not coincide, a matching method was implemented. This paper compares the simulation results arising from the choice of the weather file pertaining to the two databases. The weather files were selected within a 50 km range and 50 m elevation difference, to minimize misrepresentative results due to different climatic conditions. The models are typical of the most widespread building typology of the Italian building stock. For each model, two building fabric types were considered, the former was poorly insulated, the latter was well insulated thanks to an advanced refurbishment activity. Simulations were carried out with the EnergyPlus software.