Indoor air quality affects comfort, health and performance of buildings occupants. Chemical assessments and sensory assessments of indoor air quality contribute comprehensive knowledge on the state of the indoor environment. Fresh air without harmful pollutants is a prerequisite for a quality internal environment. This aim of the contribution is to emphasize the importance of ventilation intensity on the quality of the indoor environment. Chemical and sensory assessments of indoor air quality were done in the standard university classroom before and after the lesson. The impact of ventilation intensity on perceived air quality was studied. The experiment was performed for three levels of air exchange rate (0.50, 0.75 and 1.00 h -1). Chemical evaluation involves monitoring the indoor air temperature, relative humidity, CO2 and Total Volatile Organic Compounds (TVOC) concentrations. Sensory quality assessment is based on air acceptability, odour intensity and percentage of dissatisfied. Air acceptability raised and odour intensity decreased when ventilation intensity was increased. Perceived Air Quality (PAQ) is an important factor in assessing the indoor environment.