Mold in Air Conditioning Units


Although many residential homeowners have a tendency to feel that they may have mold within their air conditioning system, this is typically an unusual occurrence.  Mold must have the following ingredients to initiate growth and survive.

  1. A mold spore must be present to start the colonization of any mold growth.  Mold is a living organism and will initiate in the atmosphere outside of the home.
  2. Mold must have warmth to propagate and continue to thrive.  Without warmth, the mold will die away and not multiply.
  3. Mold must have some type of moisture to survive.  This moisture could be from a condensate drain, condensation within a system, a leaking roof, siding, window flashing, etc.
  4. Mold must be able to eat.  Any type of cellulose material or organic material will be food for mold.  This is the reason that the paper on the two sides of a sheet of sheetrock is so susceptible to mold growth.  The paper, cellulose, is a perfect nutrient or food for the mold spores.

Without the ( 4 ) items noted, mold will not survive, therefore, your HVAC system is not a good environment that would normally encourage mold growth.  

In most cases, the black or dirty debris that is witnessed within HVAC systems, is merely dust and accumulated dirt that has been sucked into the system from the interior environment of the home.  This is the primary reason that many interior diffusers, or wall and ceiling registers will eventually show a layering of dirt or dust around the opening of the diffuser. In most instances, this is merely dirt and dust and can be easily vacuumed off the surface.

Common sense will tell you that the cleaner the ductwork and the HVAC system, the less chance that an environment for mold growth will occur.  Periodic scheduling of ductwork cleaning and vacuuming will reduce the chance of any mold growth and eliminate your concerns. Frequent changing of air filters within the HVAC system will also reduce the opportunity for mold growth.  

It is recommended that air filters within your HVAC system be replaced each heating and cooling cycle.  If you replace filters in the fall, in preparation for the heating season, and then again in the spring in preparation for the cooling season, you should be in good shape.

If you have formally identified mold within your HVAC system, this can be confirmed  by a mold testing, then the most common method of removal and cleaning is to hire a professional duct cleaning company that specializes in the cleaning and removal of dust and mold.  Once the removal has been completed, a review of the four ingredients that are required to allow mold to reoccur is recommended.

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