An analytical model for indirect evaporative heat exchangers has been developed via a modified log mean temperature difference (LMTD) method designed for sensible heat exchangers. The original LMTD method is judiciously modified to extend its computing method to indirect evaporative cooling systems where latent heat transfer is involved. The analytical model is validated by comparing its prediction of thermal performance with experimental data of a counter-flow dew-point evaporative cooler and a cross-flow indirect evaporative cooler. Predictability of the modified LMTD method has a maximum discrepancy of +/- 8% when compared to experimental data. The model has been demonstrated to be a practical method to provide an accurate result with a short computational time. Several case studies are structured to illustrate that the modified LMTD method is suitable for designing and analyzing indirect evaporative heat exchangers. (C) 2014 Elsevier Ltd. All rights reserved.