Over the past few decades, exposure to indoor air pollutants has increased due to a variety of factors, including the construction of more tightly sealed buildings that reduce fresh air exchange to save energy, the use of synthetic building materials and furnishings, and the use of chemically-formulated personal care products, pesticides, and housekeeping and teaching supplies. Four basic factors affect indoor air quality. The HVAC system includes all heating, cooling, and ventilating equipment serving a school. Ideally, a properly designed and functioning HVAC system controls temperature and humidity to provide thermal comfort, distributes adequate amounts of outdoor air to meet ventilation needs of school occupants, and isolates and removes many pollutants through pressure control, filtration, and exhaust fans. Not all HVAC systems are designed to do all of these things.
Some buildings rely on natural ventilation, such as windows and normal air leaks in the buildings.
Others lack cooling or have little or no humidity control. There are some basic methods for lowering concentrations of indoor air pollutants. The best way to prevent indoor air problems is to keep unnecessary pollutants out of the school building. Some building codes specify the amount of outdoor air that must be continuously supplied to an occupied area. When painting, or in the event of a chemical spill, temporarily increasing the ventilation can be useful in diluting the concentration of fumes in the air.