Indoor air quality (IAQ) is measured with humidity meters and temperature andCO₂ sensors to ensure standards for human comfort indoors. Although human comfort depends on an interaction of multiple variables, optimizing relative humidity, temperature and CO₂ by measuring indoor air quality (IAQ) satisfies the comfort requirements for a wider variety of occupants than optimizing only temperature.

How does humidity affect indoor air quality? Low relative humidity in indoor air results in human discomfort. Headache, irritated eyes, sore throat, and dry skin are all symptoms of a dry indoor environment. Dry air lowers the natural defense against airborne infections and makes people vulnerable to the attack of viruses and other micro-organisms. In addition to the problems associated with low humidity, too high humidity can also cause problems. These problems are related to the growth and spread of unhealthy biological pollutants and to the damaging effect of moisture on the construction materials.

How do CO₂ levels affect indoor air quality? Demand-controlled ventilation (DVC) functions by controlling ventilation according to how many people occupy a space. The aim is to provide good indoor air quality to the occupants with energy efficient ventilation.

The European EN standard 13779: 2007 defines good indoor air quality as follows: “Indoor air quality can be categorized by CO₂ concentration.” This notion sets the foundations to operate DCV by measuring CO₂ and controlling ventilation accordingly. The standard also sets the normal expectation for indoor CO₂ level at 400–600 ppm, which is slightly above the normal levels in outdoor air (400 ppm). The modern ventilation systems are built around this supposition to ensure good enough indoor air quality while remaining energy efficient.

When indoor CO₂ levels rise, cognitive skills, like crisis response, information usage and strategy, are decreased only to 20% in a 1,400 ppm concentration of CO₂ compared to the normal outdoor level of 400 ppm. Some of the more mechanical skills, like information seeking and task orientation, are not affected much. However, cognitive skills that require more advanced application of information, information are affected the most. Handling more advanced tasks becomes much more difficult when the indoor carbon dioxide levels rise. Accurate measurement of indoor air and better ventilation are vital to cognitive abilities of people working in offices.