The following is taken from the 2006 edition of Assessment, Cleaning and Restoration of HVAC Systems, published by the National Air Duct Cleaners Association.

Maintaining clean heating, ventilation and air-conditioning systems is an important part of sustaining acceptable indoor air quality.

When an HVAC system is a source of contaminants introduced into occupied spaces, properly performed system-cleaning services should take place to reduce or eliminate contaminant introduction.

Contaminants in HVAC systems may take many forms. Common contaminants include dust particles, active bacterial or fungal growth, debris from rusted HVAC components, manmade vitreous fibers, mold spores and other items.

Experience has shown that very few - if any - HVAC systems are free of all particulates. In fact, particle deposition on component surfaces starts before the HVAC system is even installed. Airborne particles in factory settings and assembly areas are likely to settle on air-handling components and fiberglass insulation, as well as adhere to the surface of metal components.

The original installation process will subject the HVAC system to even more contamination. Construction sites contain a significant amount of airborne concrete dust, gypsum dust, sand particles, biological particulate aerosols and many other airborne contaminants in the ambient air. These particles often settle on or within the HVAC system during construction.

After the HVAC system is installed and its operation begins, the particulate-accumulation process continues throughout the life of the system. Poor design, installation and maintenance practices, low-efficiency air filtration, airflow bypass, inadequate or infrequent preventative-maintenance practices, humid conditions and many other factors will result in contaminated HVAC systems. HVAC systems may also serve to transport and redistribute unwanted particles from other sources in the building.


HVAC cleaning services have been available since the early 1900s. However, it was not until the 1970s that growing public concern for better IAQ led to an understanding of the importance of cleaning HVAC system components. Public awareness has increased ever since.

Greater demand for HVAC cleaning resulted in dramatic growth for the HVAC system cleaning industry, both for firms offering service as well as those providing research and knowledge of HVAC system cleaning and its impact on indoor air quality. This ultimately led to the creation of industry standards, training and certification programs for HVAC system cleaning professionals.

This standard defines procedures for assessing the cleanliness of HVAC systems and for determining when cleaning is required.

This standard sets acceptable criteria for the safe and effective cleaning and restoration of HVAC systems and components. It also defines environmental engineering principles necessary to control the migration of HVAC system particulates.


This standard provides test methods for verifying HVAC component cleanliness upon the completion of a cleaning project. This standard defines procedures as necessary to allow HVAC system cleaning work to be performed in accordance with the requirements of IICRC (the Institute of Inspection, Cleaning and Restoration Certification) S520, “Standard and Reference Guide for Professional Mold Remediation.”

The requirements set forth in this document address cleaning, building use, contaminant type, worker and occupant health and safety, and project monitoring.

This standard identifies construction methods and material performance criteria for the safe and effective creation and installation of new service openings used to facilitate the inspection and cleaning of HVAC systems.

It is the intent of this document to provide consumers and specifiers of HVAC system cleaning and restoration services with information needed to help ensure that cleaning is performed to acceptable standards and in such a manner that the services contribute to improved system cleanliness and/or system performance.

This standard also defines the requirements necessary to construct and install service openings in HVAC systems.

For more information on ACR 2006, write to NADCA, 1518 K St. N.W., Suite 503, Washington, DC 20005; see on the Internet; or call (202) 737-2926.