Mold in Ducts

Sometimes you will find mold in ducts, where it can be invisible to a building’s occupants. Air ducts are often round or square bare metal carrying warm or cool air to regulate the temperature of buildings. This can lead to condensation on the outside of the duct, where it is visible, or on the inside of the ductwork where it can be spread throughout the occupied space. Cooling coils, condensate pans, filters and humidifiers are often HVAC sources for moisture buildup, with the accompanying possibility for mold growth.


Testing for Mold in Ducts

Mold testing within the ductwork can be tricky. It requires some level of training, both in  gathering samples and in interpreting the results. Duct cleaners can visually inspect for mold in ducts by cutting holes in the ducts, which they later seal, or through existing access doors. They also sometimes will use borescopes, video cameras, and other high-tech gear for mold inspection. Once mold has been identified, it must be cleaned but the underlying cause for the growth must also be eliminated or the mold growth will merely reoccur.

Mold in ducts: interior viewRemoving Mold from Ducts

Removing mold in ducts requires professional mold abatement. It is often not enough to insert a vacuum device, which would stir up dust and loose dirt particles. Some mold in ducts must actually be scrubbed. Fortunately, there is a host of tools that can be used, most of them developed within the last few years. Some use soft fiber-like whips that won’t damage the ducts to scrub the mold so that it can then be vacuumed and removed.

Flexible duct and nonmetallic duct, found in some buildings, is not as easily cleaned. Extra care has to be taken so that this often fragile ductwork is not damaged in the cleaning process.

Safety Vs Effectiveness of Biocides

There is some question regarding the safety and effectiveness of using biocides in mold remediation. Some duct cleaners refuse to use any of these chemicals at all, both because they don’t want to assume the liability and because the ultimate effects of these chemicals on building occupants isn’t always clear. Others claim they are safe and effective, when used as directed, and may be necessary to thoroughly cleaning the ductwork—that vacuuming alone won’t do the job.

Some of these chemicals will continue to kill microbes and mold spores long after the ductwork has been cleaned. But the dead mold spores should still be removed. It is necessary to clean up mold contamination, not just to kill the mold. Dead mold is still allergenic, and some dead molds are potentially toxic. Use of a biocide, such as chlorine bleach, is not recommended. It doesn’t completely rule out use of biocides by professionals, if done with the proper care and guidelines.

Any chemicals can be considered harmful if misused, however, and not all air duct cleaners can be considered to be properly trained in their use. Some duct cleaners also are offering antimicrobial coatings that remain in place after they have cleaned the ductwork to discourage future mold growth.

We suggest using a National Air Duct Cleaning Association (NADCA)  member that is trained and certified. The NADCA has standards and guidelines for cleaning that members are obligated to adhere to.