Controlling the source of contaminants is fundamental to any IES strategy. Today, microbial contamination, in the form of mold and mildew, is a major indoor pollutant, but it certainly is not the only source. Indoor contamination can also be in the form of particles or chemicals. They may come from building occupants and their activities, be emitted from furnishings and wall coverings, or be brought into the building with the intake air from outdoors. Controlling these contaminants at the source is typically a much more cost-effective strategy than filtering or diluting them once they are inside the building.

Microbial contamination (fungi and bacteria) can also be a major source of indoor contamination. Microbiological colonies can grow in or on various building elements and furnishings, including carpets, ceilings, sheetrock walls, and within the HVAC system.

What can be done to reduce the potential for microbial growth inside buildings? Proper selection and specification of building materials and HVAC equipment and refurbishment per ASHRAE standards are key places to start. Air-handling equipment characteristics that significantly reduce the likelihood of the HVAC system becoming a source of microbial contamination include: