The paper presents the results of the analysis of the hot water supply system parameters. The analysis was made for 12 hot water supply systems of residential buildings connected to the district heating system. For the research, residential buildings situated in Riga and constructed in the period from 1967 to 1991 were chosen. These arc multistorey apartment buildings related to series No 119, 602, and 31 8 as well as to the special design, which have various engineering and technical solutions for the hot water-supply system. The residential buildings related to the corresponding series have the same number of sections and storeys, and the same parameters have been adjusted in the individual heat transfer stations: the hot water supply temperature has the constant value of +55 °C within 24 hours. The residential buildings were divided into two groups: the first group - houses, in which the hot water supply systems were partially renovated, and the second group - houses, iii which the nonnative service life of the hot water-supply system distribution pipelines has expired. The dynamics of the hot water consumption in the most characteristic days, the heat energy consumption for preparing I rn3 of hot water as well as the heat losses in the system were analyzed.