This study investigated the thermal performance of energy active windows (EAW). The obtained U-values of the studied EAW were compared to state-of-the-art triple-glazing windows (TGW) during a heating season. Simulation software, Matlab, was used for analytical heat transfer modeling of the studied window- types and to illustrate temperature gradients across the windows. The main objective was to evaluate how lower U-values during the coldest winter hours can be achieved to potentially shift peak heating loads of buildings. Generally, it was shown that the EAW had lower U-values compared to conventional TGW. It is concluded that windows, which have always been considered as a heat sink in constructions, can maintain building energy requirements while improving the indoor environment quality, the aesthetics, and natural lighting in buildings if replaced by EAW.