Evaluating residential air duct cleaning and IAQ: results of a field study conducted in nine single family dwellings.

A nine-home field study was conducted to investigate the impact of mechanical air duct cleaning (ADC) methods on indoor air quality (IAQ) and system performance. ADC services were provided by the National Air Duct Cleaners Association (NADCA). Only mechanical ADC methods were evaluated. Surface treatments, such as biocides or encapsulants, were not part of the study. Pre- and post-ADC measurements were used to evaluate impacts. These included deposited duct dust measurements, airborne particle and fiber concentrations, microbial bioaerosol and surface sampling, and system performance factors such as temperature, relative humidity air flow rates, and static pressure. Surface sampling in ducts indicated that mechanical ADC is effective in removing adhered dust and dirt. The particle measurement data could not offer a clear indication that indoor levels can be reduced using mechanical ADC because there was an apparent strong influence from outdoor particle mass concentrations. Mechanical ADC did not significantly reduce bioaerosol or microbial density in the houses studied. Measurements of system performance factors suggest that ADC may have a positive effect. Supply air rates increased between 4 and 32% in eight of the houses and return air flow rates increased 14 and 38% in two of the houses.