In this work, a prediction equation is proposed that determines performance parameters of fouled power systems as long as heat transfer in the two-phase region is dominant. Fouling was simulated by degrading the overall conductance. Dimensional analysis was used to reduce the problem to seven Pi groups. Since behavior found in endoreversible systems is often imitated by real systems, the endoreversible case was used for initial demonstration followed by a simulated Rankine cycle. Using an example problem, during degradation of the overall conductance, the observed parameters were found to behave logarithmically. Prediction was done by combining data under specified conditions for finite thermal capacitances. This type of model can offer benefit through saving both money and time by decreasing required number of experiments and/or simulations as well as in planning better cleaning schedules. (C) 2016 Elsevier Ltd. All rights reserved.