This paper presents the results of measurements of thermal performance of 8 heat exchangers with parallel helical coils. Measurements were conducted in substations in 2 district heating systems in Serbia: Belgrade and Sremska Mitrovica. The values of fouling resistances were found to be slightly lesser than usual values for typical shell-and-tube heat exchangers with straight tubes. Analysis of thermal performance of heat exchangers showed that the shell-side heat transfer coefficient can be calculated using the correlation based on hydraulic diameter. (C) 2012 Elsevier Ltd. All rights reserved.