Measurements in practice have shown that the level of CO2 concentration when using a ventilation unit with heat recovery is less than half. In the most critical time period, the unit maintained the CO2 concentration at the limit of 1,500ppm – i.e. at the level of hygienically permissible CO2 concentration in the school classroom during classes. The heating power of the unit is sufficient even in the critical winter months with minus temperatures. Note: The building is not insulated. The internal climate inside the classroom has subjectively (emotionally) significantly improved. The XROOM decentralized ventilation unit is the ideal solution for forced ventilation with heat recovery. Its advantage is easy assembly. The unit is light and does not need to be lifted. It does not take up additional space in the space and enables heating and cooling. Its autonomous operation does not require further intervention by the operator. The operation of the unit can also be controlled by a superior building management system (BMS/ModBus). Through a questionnaire survey among students and teachers, it was found that the unit does not interfere with teaching due to its quiet operation.