While sanitizing and disinfecting ductwork seems like a no-brainer to the untrained consumer — especially in light of guidance from the World Health Organization (WHO) about airborne transmission of the coronavirus — what, exactly, constitutes disinfecting and sanitizing ductwork?

Mark Zarzeczny, ASCS, CVI, NADCA President, has seen online advertising for sanitizing and disinfecting ductwork — something that HVAC contractors legally cannot say in the United States. Other countries, like Italy, allow these terms when referring to certain types of duct cleaning techniques.

There are clear regulations regarding the use of chemicals — often used in a disinfection process — in duct cleaning. “I see a lot of people out there saying that they’re able to magically throw a chemical in the ductwork,” Zarzeczny said. The safety of these chemicals, and the proper application, is a critical component of effective and legal use.

If antimicrobials, including sanitizer, disinfectants, and fungicides are used in a manner inconsistent with their labeling, this is considered a violation of federal law in the United States under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA).

NADCA worked with the US Environmental Protection Agency (EPA) and other parties to create the white paper, “Using Chemical Products in HVAC Systems: NADCA Provides Guidance,” which gives HVAC technicians guidance when it comes to sanitizing and disinfecting ductwork. It specifically addresses the use of chemicals during HVAC system cleaning, and provides guidance for consumers, regulators, and remediation professionals. It also gives readers an overview of products and cleaning techniques related to chemical product applications in HVAC system maintenance.

According to the white paper, a sanitizer is often misunderstood and misused. A sanitizer is a substance or mixture of substances that kills a high percentage of bacteria on a surface (99.9%), but not all of it. The EPA defines a sanitizer as a substance or mixture of substances that reduces the population of a bacterium in the inanimate environment, in “significant numbers, but does not destroy or eliminate all bacteria.”

Similarly, the legal definition of disinfectant states that the chemical “eliminates a specific species of infectious or other undesired microorganism, but not necessarily bacterial spores, in the inanimate environment only.” Disinfectants are useful to combat fungi, viruses, and bacteria.

Educating customers about source removal and the efficacy of the equipment and techniques is an important part of any job. “I always tell my customers what we’re going to do. The first thing we’re going to do is what we do best, source removal,” Zarzeczny said. “So, utilizing our equipment correctly, and just based on the cleaning alone, we’re going to remove a lot of the contamination.”

If using chemical application, and depending on the circumstances, occupants may need to leave the building to allow for adequate ventilation and time to allow any fumes to dissipate. It may take anywhere from two to eight hours for fumes or scents to fully clear out of the building.

Zarzeczny also advises explaining how chemicals and antimicrobials need time to settle to do their job. “For instance, when you spray something on the surface in your kitchen, if you read the directions on that particular chemical or cleaning product, it often says to let it sit a few minutes. The same is true for cleaning agents utilized in ductwork and on components.”

It is imperative that technicians not claim to be disinfecting or sanitizing ductwork; because the chemicals are not 100% effective, the end result will not be disinfected or sanitized ductwork.

In addition, technicians should advise customers that once the system is turned back on, the ductwork may become contaminated once again due to a variety of reasons outside of the technician’s control. “Once you turn that system on, we cannot control it because you have a return, you have fresh air intakes that bring air into those systems, and it can certainly recontaminate your ductwork,” Zarzeczny said.