The aim of the present study is analysis of heat energy consumption in public buildings (managed by Riga city municipality) in year 2008. Our data set contained information on more than 400 public buildings, including data on heat energy consumption depending on building use, and data on the quantity and quality of windows in these buildings. The data were analysed across ten groups of buildings managed by the municipality: schools, special status buildings, day care centres, hospitals, libraries, churches, recreation centres, local government buildings, museums, and shelters. The largest groups were schools (more than 100 analysed units) and day care centres (also more than 100 analysed units). Our analysis focuses on comparing heat energy consumption in buildings with new 2-glass packet windows with PVC frame (heat transfer coefficient U≤1,8 [W/(m2*K)]) and in buildings with old 2-glass windows with wooden frame (U≥2,5 [W/(m2*K)]). In addition, we compared heat energy consumption in buildings with windows covering more than 20% vs. less than 20% of the building facade. We analysed the data for each group separately. Our analysis shows that mere windows change, without an appropriate renovation and modernisation of the ventilation system, does not lead to any significant economy of heat energy. In some cases, it can even result in an increase of energy consumption.