In a water heating system, such as a district heating and hot water supply system, the composite fouling of CaCO3 and CaSO4 characterizes the actual usage environment. In this study, the composite fouling characteristics of CaCO3 and CaSO4 in plate heat exchangers were measured and analyzed at various concentrations, flow velocities, temperatures, and chevron angles. Moreover, based on the measured data, empirical correlations for the fouling resistance, fouling period, and pressure drop ratio at an asymptotic state, are developed as a function of concentration, Re, temperature, and chevron angle. The correlations for the fouling resistance, fouling period, and pressure drop ratio at the asymptotic state yield satisfactory predictions with mean absolute errors of 7.1%, 4.6%, and 2.0%, respectively. In addition, the sensitivities of the operating and geometrical parameters on the composite fouling characteristics are analyzed using modified regression coefficients. (C) 2019 Elsevier Ltd. All rights reserved.