Should chemical biocides be applied to the inside of air ducts?
Air duct cleaning service providers may tell you that they need to apply a chemical biocide to the inside of your ducts to kill bacteria (germs), and fungi (mold) and prevent future biological growth. Some duct cleaning service providers may propose to introduce ozone to kill biological contaminants. Ozone is a highly reactive gas that is regulated in the outside air as a lung irritant. However, there remains considerable controversy over the necessity and wisdom of introducing chemical biocides or ozone into the duct work. Little research has been conducted to demonstrate the effectiveness of most biocides and ozone when used inside ducts. Simply spraying or otherwise introducing these materials into the operating duct system may cause much of the material to be transported through the system and released into other areas of your home.
In the meantime...
Before allowing a service provider to use a chemical biocide in your duct work, the service provider should:
Before allowing a service provider to use a chemical biocide in your duct work, the service provider should:
1. Demonstrate visible evidence of microbial growth in your duct work. Some service providers may attempt to convince you that your air ducts are contaminated by demonstrating that the microorganisms found in your home grow on a settling plate (.e., petri dish). This is inappropriate. Some microorganisms are always present in the air, and some growth on a settling plate is normal. As noted earlier, only an expert can positively identify a substance as biological growth and lab analysis may be required for final confirmation. Other testing methods are not reliable. 2. Explain why biological growth cannot be removed by physical means, such as brushing, and further growth prevented by controlling moisture.
If you decide to permit the use of a biocide, the service provider should:
1. Show you the biocide label, which will describe its range of approved uses.
2. Apply the biocide only to uninsulated areas of the duct system after proper cleaning, if necessary to reduce the chances for regrowth of mold.
3. Always use the product strictly according to its label instructions.
While some low toxicity products may be legally applied while occupants of the home are present, you may wish to consider leaving the premises while the biocide is being applied as an added precaution.
Do sealants prevent the release of dust and dirt particles into the air?
Manufacturers of products marketed to coat and seal duct surfaces claim that these sealants prevent dust and dirt particles inside air ducts from being released into the air. As with biocides, a sealant is often applied by spraying it into the operating duct system. Laboratory tests indicate that materials introduced in this manner tend not to completely coat the duct surface. Application of sealants may also affect the acoustical (noise) and fire retarding characteristics of fiberglass lined or constructed ducts and may invalidate the manufacturer's warranty.
Questions about the safety, effectiveness and overall desirability of sealants remain. For example, little is known about the potential toxicity of these products under typical use conditions or in the event they catch fire.
In addition, sealants have yet to be evaluated for their resistance to deterioration over time which could add particles to the duct air. Most organizations concerned with duct cleaning, do not currently recommend the routine use of sealants in any type of duct. Instances when the use of sealants may be appropriate include the repair of damaged fiber glass insulation or when combating fire damage within ducts. Sealants should never be used on wet duct liner, to cover actively growing mold, or to cover debris in the ducts, and should only be applied after cleaning according to appropriate guidelines or standards.
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