Abstract Thermal storage systems with phase change materials offer a high density of energy with a moderate temperature variation as well as the possibility to keep the inner temperature within a comfort range. To achieve this goal, it is necessary to select the most suitable phase change material. In this line, numerical simulations are necessary to predict results and take decisions about the best material that will be implemented on buildings devices for thermal performing. This work aims to study numerically how the inner air temperature of a defined room changes when a double-glazed PCM-filled window is mounted. For this, a new methodology for latent heat was implemented by a temperature-dependent Gauss-function, while an on/off strategy was considered to separate solid from liquid state. Both equations and parameters that involve thermophysical and optical properties were determined experimentally by Modulated Differential Scanning Calorimetry and spectroradiometer techniques, respectively. The resultant numerical model was implemented into the Simusol software for first time. It was found that the inner air temperature can be reduce up to 40% in average, in comparison with empty double-glazed window case, making it possible to reach the expected range of 20–26 °C. Simulation results also revealed that volumetric air flow for HVAC systems could be reduced up to 87% in winter, when PCM is implemented.