The purpose of this study is to compare the heating energy requirements according to the window performance and derive standard coefficients that can be used to easily calculate the savings. In Korea, the total amount of energy consumed by buildings is restricted by the Green Building Creation Support Act and building standards for the energy-saving design have been proposed. In addition, the energy-saving design criteria for buildings suggest insulation performance standards for windows and doors to prevent heat loss in buildings. Windows are the most important area of heat loss in the main building, and are a priority target for energy efficiency. High-efficiency insulating windows can reduce the heat load by minimizing the amount of energy loss through the application of a thermal bridge blocking material for double-glazed windows and window frames. Therefore, in this study, the effect of the change in window performance on the heating energy demand was checked using the building energy evaluation software ECO2, and standard coefficients for calculating the reduction rate were derived.