This paper investigates the wet-surface ®n eciency of a plate-®n-tube heat exchanger. Depending on the compromise made between accuracy and complexity, a one-dimensional analytical model, a onedimensional numerical model and a two-dimensional numerical model are proposed respectively for ®n eciency together with the corresponding computation algorithms. The one-dimensional numerical model considers the local mass transfer eect. The two-dimensional model takes into account of the complex ®n geometry and the variation of moist air properties over the ®n. In the analytical model, two parameters M Ã and T Ã a are employed in the solution in place of the C parameter that is commonly used in the literature. A quantitative comparison of these models together with a widely used method by McQuiston is presented. Meanwhile, the ®n performance of a plate-®n-tube heat exchanger is investigated under a variety of ®n geometric parameters and air¯ow conditions, especially for a wide range of air relative humidity (from 20 to 95%). Due to the dierent simpli®cations made in each model, the dierences among the calculation results are found to be signi®cant. Finally, the applications and limitations of these models are discussed along with the error analysis.