The indoor climate of educational institutions (kindergartens, secondary schools and universities) in Estonia is investigated. The main hazards for students’ health are: the high concentration (over 800 ppm) of carbon dioxide in the classrooms that refers to the inappropriate ventilation; the non-ergonomic computer workplaces where the direction of the natural light (without blinds for the windows) is causing glare on the monitors; the low humidity of the air in winter; the low air temperatures in the classrooms in winter and high temperatures in the warm season. The recommendations for technically and economically effective improvement possibilities are given.