The invention relates to a method for improving energy efficiency of heating systems in buildings, in which method at least one measuring sensor is installed in all apartments of a building to collect data that will be used a basis for adjustment measures of the heating system. In the method, measurement data obtained from the measuring sensors is analysed by means of a suitable algorithm and, on the basis of the measurement data, apartments best suited for adjustments are searched for. On the basis of the analysis and the search, apartments best suited for adjustment in terms of overall cost-efficiency are selected.