White Paper Discusses Ventilation Pathogen Transmission Reduction

In a new white paper, “Return Ductwork Requirement for Airborne Pathogens Through the Airstream,” experts discuss the reduction of pathogen transmission using a building’s original mechanical design, original installation, design intent and proper maintenance by a skilled, trained and certified technician. Two approaches a building engineer has at their disposal to reduce pathogen transmission are pressure barriers and airflow distribution.

The white paper discusses the pros and cons of using the cavity above a finished ceiling as a return air plenum combined with supply air to the air handler as a proper ventilation technique.

Considerations include how ventilation systems affect the health and well-being of building occupants, as well as HVAC workers. For instance, while a ceiling plenum provides some fan-specific energy efficiency and a reduction in material and labor costs, it could put occupants and workers at risk and result in unintended energy losses.

With a negative ceiling plenum, negative-pressurized architectural plenums can draw in untreated and humid outside air through the building’s skin or roof or unconditioned air from untreated spaces. That untreated air must then be treated at a cost of energy.

A ducted return system allows a testing, adjusting and balancing professional to alter room pressures and airflow patterns to accommodate a change in use or mitigate pathogen transmission during a pandemic. There also are additional safety concerns regarding daily maintenance tasks, source control and the introduction of additional airborne particulates that may compromise indoor air quality. An open ceiling plenum is difficult to clean and disinfect, while ductwork can be easily cleaned.

Authors of the white paper include members of the American Society of Heating, Refrigerating and Air-Conditioning Engineers Technical Committee 5.2 Duct Design, which has officially approved the document. For more information, visit

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