Abstract
Since the COVID-19 outbreak, special attention has been paid to proper ventilation and building management systems. The indoor air CO2 concentration level is still used as an effective indicator to evaluate indoor air quality. Many different sensors have appeared on the market in the last two years. However, calibration procedures and guidance on proper installation have not been well described by manufacturers. The research method is based on a review of technical parameters. The practical measurements of CO2 concentration were taken using different sensors. For these purposes three different premises were selected. It was found that CO2 measurement failure happened in residential buildings without mechanical ventilation. Meanwhile, in well ventilated buildings all sensors have shown similar results and the difference between sensors located in different zones was minimal.