This paper describes how the effectiveness of a single pass, two stream plate heat exchanger (PHE) can be calculated when one stream undergoes a phase change; specifically condensation. Analytical solutions are given for the system under the assumption of constant overall heat transfer coefficient when run in either co-current or counter-current arrangements. The analysis is then extended to systems in which the overall heat transfer correlation is dependent upon the quality of the phase change stream and a simple methodology is developed to predict the performance of the PHE in these situations.