The National Air Duct Cleaners Association (NADCA), also known as the HVAC Inspection, Cleaning, and Restoration Association, published a white paper on methods of inspecting and cleaning open air plenums. The paper addresses common contaminants found in open air plenums that can adversely impact the conditioned space, and provides guidance for the inspection and cleaning of those areas.
Open air plenums are found in both commercial and residential settings and consist of intended non-ducted air pathways formed in building cavities, voids, and spaces outside of the occupied zone of buildings. By design, they facilitate airflow between HVAC equipment and the occupied space of a building, and often contain building elements such as mechanical (HVAC), electrical, plumbing, gas piping, fire protection, sewer, and telecommunications systems that are essential to the operation of the building or residence.