Currently, special care is given to determining the performance of windows and meeting the requirements of buildings. In terms of energy efficiency and building economy, window design and the selection of appropriate glazing systems are significant. This paper deals with double-glazing window units that are composed of, respectively, tinted glass, clear reflective glass, low emissivity (low-e) glass, and smart glass-one surface consisting of a high-performance heat-reflective glass and the other surface with a low-emissivity coating, which reduces the heating and cooling loads of buildings by providing both solar control and heat conservation. This study is aimed at investigating the effects of these different alternative units, instead of readily, available double-glazing units, in two flats that have the same construction and operation system, but with a different plan type, on building energy consumption and building economy in terms of a life cycle cost analysis. For study, Ankara is selected, as it has a cold climate, in Climate Region III of Turkey. F- and C- type high-rise residential blocks with flats with two and three bedrooms, respectively, constructed by the Republic of Turkey Prime Ministry Housing Development Administration of Turkey -TOKİ in Ankara, are used as models for the simulation. The flat plans in these blocks are modelled by means of DesignBuilder 1.8 v energy simulation software.