Good air quality does not always require extensive technical systems. In this recent article in the specialist magazine nbau, the authors discuss why natural ventilation—illustrated through examples from school buildings—often proves to be the more robust solution. Thomas Auer, Felix Thumm, and Martin Gabriel (ENIANO GmbH, München) show that although the historical threshold of 1000 ppm is deeply rooted in building engineering, meeting it in schools demands significant technical upgrades, high costs, and intensive maintenance. At the same time, studies indicate that people’s subjective perception of air quality often does not align with CO₂ measurements: mechanically ventilated rooms are frequently described as “stuffy” despite low values, while naturally ventilated classrooms with considerably higher concentrations are perceived as pleasant.
The article explains that CO₂ has no toxicological relevance within typical indoor ranges. It merely indicates how many people are in a room and how well it is ventilated. Other crucial factors—such as VOC emissions from materials, fine dust, or odors—are not captured by CO₂ measurements. On top of that, many sensors are inaccurate, drift over time, or do not measure actual CO₂ at all—leading to frequent misinterpretations in schools. The often‑quoted 1000‑ppm value is therefore primarily a comfort guideline, not a medical threshold.
Mechanical ventilation systems with CO₂‑controlled demand‑controlled ventilation (DCV) are considered energy‑efficient, but in practice they often fail to perform as intended. Sensors require regular calibration, which rarely happens in everyday school operations. Incorrect measurements lead to incorrect control responses, higher energy consumption, and a so‑called performance gap: the promised savings fail to materialize while maintenance and operating costs rise. Every additional technical component also increases the likelihood of malfunctions.
The authors argue that school buildings should rely more on natural ventilation, low‑emission materials, and simple usability. Mechanical ventilation is only necessary in specific cases. In many schools, responsibility for air quality can be placed in the hands of the users—provided the building is well designed. Natural ventilation is not always perfect, but it is sustainable, cost‑effective, and often closer to what users actually perceive as “good air.”