This article examines long-term patterns in energy performance of windows. It presents energy balance calculation results of window glazings in cardinal directions in the Estonian climate representing the Nordic climate in general. Measured climate input data of 43 years were used in addition to standard energy calculation years. The energy balance of five different glazing types was compared during the heating period of October to March. Calculations were made according to the EU standard ISO 13 790. It was found that southern facing glazings with reduced solar to thermal transmittance ratio higher than 0.63 m(2) K/W can have positive energy balance over the sum of the heating period. Two of the selected glazings exceeded this level and achieved positive energy balance over the heating period in all years. On the other hand, glazings in the other cardinal directions predominantly were found to experience negative mean energy balance over the sum of the heating period. In the maximization of energy and economic efficiency, this sends the message to architects that, under certain conditions, optimization constraints are more important in some cardinal directions than in others. Such results support scientifically-informed decision making by practitioners at early design stages, for optimal energy efficiency. (C) 2014 Elsevier Ltd. All rights reserved.