NADCA Publishes White Paper on Inspection and Cleaning of Open Air Plenums

Posted on 01/23/2023

Air duct cleaners will inevitably encounter open air plenums — also called plenum spaces or air voids — at some point in their career. They 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 the building. By design, they facilitate airflow between the HVAC equipment and the occupied space of a building. They may exist between a structural ceiling and dropped ceiling, under a raised floor, or between walls, and they 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. 

ACR, The NADCA Standard, specifies how to approach cleaning certain types of material, but the standard does not address open air plenums specifically. Because cleaning these spaces isn’t included in the ACR, NADCA has published the new white paper to address common contaminants found in open air plenums that can adversely impact the conditioned space, and provide guidance for the inspection and cleaning of those areas.

The accumulation of contaminants in an air plenum can cause indoor air quality issues that potentially pose health risks to the occupants of the building or home, but open air plenums can be challenging and dangerous for technicians to clean since they are typically unfiltered spaces — and can contain dust, dirt, debris, asbestos, lead, animal and insect by-products, microbial contamination, and a broad range of hazardous chemicals and materials. 

Vice President of Service-Tech Corporation Florida and NADCA Board member, Paul Keller, Jr., ASCS, was instrumental in the development the white paper. “As the authority in the industry, NADCA has developed this white paper to provide recommended approaches to inspecting and cleaning open air plenums,” Keller said. “These spaces are often overlooked when cleaning HVAC systems because typical duct materials like ductboard and flex duct may not be present. Unlike sealed ductwork, open air plenums can be used for purposes other than to facilitate a pathway for air circulation, and often contain items unrelated to the HVAC system.”

Keller compares the cleanliness of the materials found in an air plenum to what you might find in an everyday junkyard. “There’s quite a lot of dust, dirt and debris that accumulate just because it’s normally an unfiltered area.” Keller said. “Also, the hazards encountered can range across a broad spectrum.”

Keller stresses that this accumulation of dust, dirt and debris in an air plenum causes indoor air quality issues that need to be addressed beyond a typical cleaning. In addition, they create an environment that can lead to microbial-control issues and carcinogenic issues.

Open air plenums should be inspected and cleaned periodically since airflow throughout these spaces can create an increased risk of contamination, odors, condensation, microbial growth, and other conditions that may require attention and cleaning. 

NADCA’s new Open Air Plenums White Paper is available for download at

Click Here to Download the White Paper

Want to learn more about cleaning open air plenums? CLICK HERE to check out a previous blog with all sorts of tips for cleaning these often overlooked spaces.