The education of energy users is one of many possibilities to reduce the energy consumption in existing multifamily buildings. Unfortunately, to the best authors' knowledge, there is no long term experimental evaluation of energy savings, which may be achieved in flats where heat cost allocators were installed. This article presents the results of experimental research conducted during 17 heating seasons (from 1997/1998 to 2013/2014) in a multifamily building located in Poland. The heat cost allocators were installed in the right part of the building (part R) in 1996 and in the left part of the building of the same size (part L) in 2011. In the summer 2005, thermal renovation of external walls of the analysed building was made. The energy consumption in part R of the building was on average 26.6% and 30.5% lower than in part L for the period before and after thermal renovation of external walls of the building, respectively. After the installation of the heat cost allocators in part L of the building, the amount of heat used for heating was also analysed. The comparison of saved energy to the cost of installing, reading, and maintaining the heat cost allocators was made. (C) 2015 Elsevier B.V. All rights reserved.