A new heat and mass transfer model based on basic principles has been developed for thermal calculations of an indirect evaporative cooler performance. Some simplifications have been incorporated to make the model more user-friendly. It is universal and can be used to analyze different indirect evaporative cooler designs and conditions. The paper also compares results from sample calculations from several designs with data from other sources for validation. This model can be used for energy analyses as well as for system or product optimization.