Minimizing thermal losses through windows and maintaining large glazing areas to provide adequate natural lighting in residential buildings are essential considerations for modern architecture, sustainability, and indoor comfort. In this study, a detailed heat transfer model for a novel energy-active window (EAW) is developed and validated to rate its thermal performance. An EAW utilizes low-grade heat to reduce building heat losses during the winter season. A thorough literature review was conducted to select the correct heat-transfer correlations for the investigated configuration. A two-dimensional finite differencing scheme was applied to approximate the vertical and horizontal temperature distribution across the EAW. Detailed temperature gradients, across the height and width of the window, were obtained. Thorough sensitivity analyses of the governing parameters were conducted to evaluate the windows' thermal performance. The results indicate that EAWs have the potential to reduce heating power demand by approximately 2.2 W/m(2) floor area and 1.3 W/m(2) floor area at outdoor temperatures of-20 degrees C and-5 degrees C, respectively, for buildings with a window-to-floor area ratio of 10%. This potential increases proportionally with the ratio. The highest thermal efficiency of EAW is achieved when the temperature of the supplied air inside the EAW is equal to or above room temperature. (c) 2020 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).