To maintain proper indoor air quality and increase energy efficiency, a demand-control ventilation (DCV) system has become a popular solution. This paper reports the findings of a field study conducted on the performance of the DCV systems in eight public buildings in southern Finland. We conducted the measurements in two stages. In the first stage, we made a site visit and measured the airflow rates in the design operation conditions of the chosen space. For the second stage, we left temperature/humidity data loggers to monitor the thermal conditions during the normal operation mode of the space. The results indicate that, out of the eight studied spaces, only one DCV system was performing according to design specifications. While the systems were operating in a suboptimal way, the flaws in functionality were mostly minor, and none of the sites had perceived indoor-air-quality-and/or thermal-condition-related problems during the time of measurement. Nonetheless, this result shows that the potential benefits of DCV were partially lost due to malfunctioning systems. Additionally, by only monitoring room air temperature (or IAQ) without airflow rate measurements in different operation modes, it is not possible to conclude whether the DCV system works properly or not.