The paper consists of theoretical-research and practical work. The theoretical-research part discusses ventilation losses in buildings, their occurrence, instructions for setting up equipment and measuring losses. The assessment of the condition of the facility "Depadans", which is located within the complex of the Special Hospital for Rehabilitation "Termal" in Vrdnik, was carried out as part of the practical part, which also includes the calculation of energy efficiency for the subject facility. The mentioned calculation was repeated for after the implementation of the proposed energy rehabilitation measures. The building was originally classified in energy label "E", and after rehabilitation it was classified in energy label "C".