This paper presents the results of an experimental study performed to obtain a simplified model applicable to two adiabatic humidification systems: wetted wires and centrifugal atomizing. The aims of this study are to provide a model to be used in situ as a diagnosis tool in the commissioning of air-conditioning systems, and to develop a comparison between “wet” and “therma” effectiveness methodologies that also can be useful for the commissioning process. The model is able to predict the exhaust dry-air temperature, exhaust humidity ratio, and the humidifier effectiveness by using as inputs the supply-air temperature and relative humidity as well as the air and water mass flow rates. Simplicity and accuracy are the crucial factors. A series of tests are performed in order to validate the model.