This paper presents the results of experimental research on 8 plate heat exchangers. Their purpose is to heat water for radiator heating system and domestic hot water. Measurements were carried out in 4 substations in district heating system in Belgrade (Serbia). The main achievement of this research was that the fouling factors were determined experimentally, and the found values can be used further on in design of plate heat exchangers in district heating systems. (c) 2012 Elsevier B.V. All rights reserved.