Heat losses through window glazing are unavoidable but can be significantly suppressed during night hours using roller blinds. Results of calculations of the effect of roller blind on heat losses from central part of double-glazing window during the night in the heating season in Central Europe are presented. The hourly meteorological data for the outdoor air temperature, wind velocity and sky temperature are used. It is demonstrated that internal roller blinds can save about 33% and external roller blinds about 45% of heat losses through a central part of the double-glazing window at the blind to glass pane spacing above 20 mm. The similar relative energy savings were obtained for the double-glazing window having low emissivity coatings, i.e. for the emissivity ? = 0.20 the internal and external roller blind can save about 29% and 44% respectively.