Mechanical ventilation systems with heat recovery are considered the most optimal systems for residential ventilation. This research focuses on decentralized ventilation which do not need any ducting. Therefore, this system is very suitable for use in retrofitting. The performance criteria of these units are similar to those of central systems. A recuperative and two regenerative ventilation units were tested in a double climate chamber where temperature, air velocity and contaminant concentration were monitored on a fixed 80 point grid. The results are reported in terms of thermal comfort, ventilation efficiency and energy consumption. The results showed that, by using decentralized ventilation, rooms can usually be efficiently ventilated at a good level of thermal comfort. The energy consumption of one ventilation unit is low, but several units have to be installed in order to adequately ventilate a residential building.