The influence of windows on the energy balance of apartment buildings in Amman is investigated by using self developed simulation software (SDS) based on the ASHRAE tables for solar heat gain calculation and coaling load factor for latitude 32 degrees, where Amman city is located. The calculations of energy saving are made to find out the influence of windows on the energy balance of apartment buildings in Amman. Also, the present investigation aimed to study the energy performance of windows of an apartment building in Amman in order to select the most energy efficient windows that can save more energy and reduce heating load in winter, the percentage of saving energy and saving fuel and money through time. Variations of type of glazing using eight types of glazing (clear glass, types A, B, C, D, E, F, and G) are made to find out the most appropriate type of glazing in each direction. Also the orientation of window is changeable in the main four directions (N, S. E and W). The area of glazing varies also in different orientation to find the influence of window area on the thermal balance of the building. The results show that if energy efficient windows are used, the flexibility of choosing the glazed area and orientation increases. It has been found that choosing a larger area facing south, east and west can save more energy and decrease heating costs in winter using certain types of glazing such as glass type A and clear glass, while decreasing the glazing area facing north can save money and energy. However, it has been found that the energy can be saved in the north direction if glass type B has been used. In the apartment building, it is found that certain combination of glazing is energy efficient than others. This combination consists of using large area of glass type A in the east, west and south direction, and glass type B in the north direction or reducing glazing area as possible in the north direction. (C) 2009 Elsevier Ltd. All rights reserved.