As air ducts age, problems can begin to occur, especially in the plenums also referred to as main ducts. Galvanized sheet metal air ducts may begin to flake. This flaking usually occurs due to oxidation from constant moisture being run over the duct. Over years of use, the galvanized coating breaks down and exposes the ducts metal to moisture creating oxidation. This causes flaking of the duct, which then is blown through the central air system and into the living space causing what may appear to be dust issues or larger pieces of debris coming from the ducts.

Another commonly used material for the plenums of air duct systems is fiberboard ducts. Fiberboard is constructed of compressed resin bonded glass fibers. The interior of fiberboard uses a seal coating to prevent fiber glass particles from being spread through the central air system. The exterior uses a foil face which creates an air and water vapor barrier. Over the years the interior lining of fiberboard ducts may begin to deteriorate. The tough conditions of constant moisture from the a/c system running, as well as the dessert like conditions of heating cycles take a real toll on the fiberboard's interior lining. Deterioration or mold problems can call for an encapsulation re-coating of the air ducts.

Encapsulation coating application to the interior of air ducts may be useful and/or necessary for various reasons. 

- To prevent the circulation of fiberglass particles into the indoor air on systems which use ducts made of fiber board.

- To re-coat the interior of ducts which have been contaminated with mold or mildew and prevent further recontamination

- To re-adhere fiberglass damaged by aging and deteriorating ducts

- To prevent the circulation of rust or oxidation particles into indoor air from metal ducts which are deteriorating 

- To remove heavy odor from air duct systems such as prolonged cigar or cigarette smoke odors as well as odors from fire       damage.

Encapsulation is a cost effective way of improving indoor air quality, and/or repairing and restoring air ducts which may otherwise need to be replaced entirely. 

Once applied, the encapsulation coating dries to form a durable, flexible, moisture-resistant protective coating that minimizes dirt buildup on the coating surface. 

Actual cost of encapsulating air ducts varies greatly, but expect to invest upwards of $300 for an average one unit, one zone air duct plenum re-coating. Air ducts must always be cleaned prior to encapsulation coating application.