The purpose of this study is to address the subject of nonroutine cleaning of ducts and other components of HVAC systems. A literature review was conducted to determine the short- and long-term environmental and occupational health aspects of nonroutine cleaning of HVAC components. Surveys were conducted of representative duct cleaning companies to determine their recommended approach to duct and HVAC system cleaning. Interviews of professionals from trade associations, academia, government agencies, and consulting firms were also undertaken to gain their assessment of the cleaning process. The means used to identify particulate and odor contamination in HVAC systems, including problems associated with the identification process, are discussed. The advantages and disadvantages of various cleaning methods in terms of the types of equipment and long-term effectiveness are described.