Mold in AC Ducts: Should You Be Concerned About Your Indoor Air?

inspecting mold in AC ducts

Depending on the age of the air conditioning system, mold in your ac ducts and air handling unit can at times be present. This should not be a surprise since an air conditioning system is a relatively wet environment.

When moisture is coupled with dust and other nutrient sources that accumulate within the system over time, mold growth will often occur, particularly inside the ac unit and supply air duct plenum.

Some mold may also appear on the cooler outside surfaces of the ac unit and supply air vents. This is due to condensation in humid areas such as garages and attic spaces. Generally, the older the ac unit and ductwork, the higher the level of mold activity on surfaces within the system.

But is mold in your ac ductwork a cause for concern for your air quality? How does an inspector check for mold in air ducts and vents?

Does Mold in Air Ducts Affect Indoor Air Quality?

Fortunately, the type and quantity of mold growth typically found inside the air ducts and outside the ac system (Cladosporium species) does not significantly impact the indoor environment in most cases. With that said, significant Cladosporium mold growth or lesser amounts of other types of mold inside or outside the system can impact the indoor air quality. It may also indicate issues with the design, performance or operation of the ac system itself.

Therefore, inspecting and testing the ac system for mold is recommended as part of any indoor air quality survey. Also if there is reason to believe there are potential mold issues related to the system.

Inspecting for Mold in Ductwork

Inspection of air conditioning systems typically involves a visual assessment and surface sampling of accessible areas (e.g., supply and return air vents, return air plenums and supply air duct boots). It also includes an air sample while the system is in operation. Sampling can also be performed within the ac unit and ductwork with the assistance of a licensed air conditioning contractor. Mold sampling within the ac vents is not typically required if there is no evidence found of elevated mold activity, whether in the air or at the accessible areas of the ac system.

If mold levels are found to be elevated in the air or surface samples, further testing of the air conditioning system is often recommended. If significant mold growth or mold species of concern are found within the AHU and ductwork, proper remediation of the entire air conditioning system will be required.

How to Prevent Mold in Your AC Ducts

The most effective way to prevent or limit mold in AC ducts is simply to keep it very clean. The most efficient way to do that, starting with a new or clean system, is to provide high-level filtration. This prevents soils from getting into the system at all.

A high-efficiency deep pleat filtration system, in our opinion, is the most effective form of filtration. This includes installing MERV 11 or 13 filters immediately before the return air enters the air handler. To help keep the return ducts clean, lower-efficiency filters can be installed at the return vents. This can also extend the life of the primary filter.

As part of our mold assessments in a property, IET (Servicing Tampa Bay, FL) can provide a general inspection of the AC system, along with checking for mold, to make sure it’s running properly and not contributing to poor indoor air quality.  Feel free to contact us.

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