Indoor air quality is not necessarily a concept that is easy to understand or define. It is a constantly changing interaction of a complex set of factors. Each of these factors must be considered when looking for an indoor air quality problem. IAQ professionals use the four listed below as a basis for every sound investigative approach. Without considering each of the following factors, simple solutions to the problems at hand could be easily missed.

• Source - There is a source of contamination or discomfort indoors, outdoors, or within the mechanical systems of the building.  ...more.

• HVAC - The HVAC system is not able to control existing air contaminants and ensure thermal comfort (temperature and humidity conditions that are comfortable for most occupants). ...more.

• Pathways - One or more pollutant pathways connect the pollutant source to the occupants and a driving force exists to move pollutants along the pathways).  ...more.

• Occupants - Building occupants are present and are affected enough to raise indoor air quality concerns.  ...more.