If you have insulated air ducts and the insulation gets wet or moldy, it can't be cleaned effectively and must be removed and replaced. If you notice that dust appears much faster and that the dust accumulation is much greater, this is a common sign that the air ducts are dirty. The increase in dust could also indicate an air leak somewhere in the air ducts, so dust and dirt are accumulating when the HVAC system works. Some service providers may also suggest applying chemical treatments (sealants or other encapsulants) to encapsulate or cover the interior surfaces of air ducts and equipment housings, as they believe that this will control the formation of mold or prevent the release of dirt particles or fibers from ducts.
In addition, the service provider may propose the application of chemical biocides, designed to eliminate microbiological contaminants, inside the ducts and in other components of the system. You can also contact professional duct cleaning service providers and ask them about the services they provide. Duct cleaning methods vary, although industry associations that deal with cleaning air ducts have established standards. Since the conditions in each home are different, it's impossible to generalize about whether cleaning your home's air ducts would be beneficial or not.
While the debate over the value of regular duct cleaning continues, there is no evidence to suggest that such cleaning is harmful, provided it is done correctly. If someone in your household has more allergy symptoms or respiratory problems, it's possible that it's due to mold, so you should check and clean your ducts right away. If no one in your household has allergies or unexplained symptoms or illnesses and if, after a visual inspection of the interior of the ducts, you see no sign that the air ducts are contaminated with large deposits of dust or mold (with no musty smell or visible mold growth), cleaning the air ducts may not be necessary. However, there is little evidence that cleaning only the ducts improves system efficiency.
If sufficient dirt and moisture are allowed to enter the duct system, there may not be a significant difference in the speed or degree of microbial growth in internally lined or bare sheet metal ducts. Air duct cleaning service providers can tell you that they must apply a chemical biocide inside the ducts to kill bacteria (germs) and fungi (mold) and prevent future biological growth. Cases where it may be appropriate to use sealants to encapsulate duct surfaces include repairing damaged fiberglass insulation or combating fire damage inside ducts. You may consider cleaning the air ducts simply because it seems logical that the air ducts will get dirty over time and, from time to time, they should be cleaned.
This is because much of the dirt in the air ducts adheres to the duct surfaces and doesn't necessarily enter the living space. Most organizations that deal with duct cleaning, such as the EPA, NADCA, NAIMA, and the National Association of Sheet Metal and Air Conditioning Contractors (SMACNA), do not currently recommend the routine use of sealants to encapsulate contaminants in any type of conduit.
