Poor indoor environment in primary schools in Sweden seems to be a problem in many municipalities in Sweden. In a report from the Swedish Public Health Agency, it is estimated that 40 percent of schools have complaints about air quality. The causes of the problems are poor ventilation, high humidity, changes that where made to the buildings, and high density of pupils in the classrooms. Improving indoor air by improvement of ventilation systems can be too costly for municipalities. In this project, we have looked at whether an installation of a large number of green plants in classrooms could change that, and even reduce energy use. There is research that shows that we feel both physically and mentally better if we are surrounded by green plants. Physically, because they can purify the air and convert carbon dioxide to oxygen. In addition, they increase the humidity and regulate the temperature. Mentally, perhaps because we are part of nature and have lived in it most of human history. The case study in this project was an elementary school located in a small rural community in the northern part of Sweden. A total of 350 green plants were installed in four plant‐stands distributed in 2 different eighth grade classrooms with about 25 students in each. A similar adjacent classroom (ninth grade) was used as a reference object without green plants. The plant‐stands were designed by industrial design students at Mid Sweden University and would result in functional prototypes with automatic irrigation. The project lasted for two semesters, the autumn semester 2019 and the spring semester 2020. Measurements of the indoor temperature showed that the green plants contribute to a more stable temperature and can even increase the temperature slightly, which can be used to reduce the need for heat. The effects on humidity were only higher in the classrooms with plants during the night when the ventilation flow was low. The carbon dioxide levels in the classrooms with the plants were 10% lower during education time compared to the control classroom, which indicates that green plants could be used to reduce the ventilation air flow and thereby reduce heat losses from exhaust air flow. The amount of airborne particles was already low and no change could be observed after the installation of the plants.