The study includes a description of the processes occurring during the recovery of sensible and total heat in heat exchangers used in ventilation systems. Example air transformations are presented on the Mollier diagram. The mechanism of moisture transfer in both hygroscopic and non-hygroscopic rotary heat exchangers is also included. The results of measurements conducted in condensation conditions in a ventilation unit equipped with a rotary non- hygroscopic rotary heat exchanger, operating in a single-family building in use, were presented. Moisture recovery with an average efficiency of 32% and temperature efficiency of 75% were demonstrated. The influence of indoor and outdoor air parameters on heat recovery efficiency was analysed, but the measurements performed did not allow for the identification of all the relationships shown in the literature.