Q: We have had mold people out who want to tear down walls to get to our smelly problem. Could it be solved in a simpler way?

A: When investigating a musty odor the primary question is: what is the source of the moisture that allowed the mold or bacteria to become established?

First does the musty odor come from the wall itself or from the ductwork of the ventilation system? The mold growing out of the vent (supply diffuser) could be from deposited dust attracted by the static electricity generated from moving air. This deposited dust can support microbial growth when cool air (degrees Fahrenheit) condenses moisture on the dust. The first suggestion is to clean/disinfect the supply diffuser so that if moisture does condense on the supply diffuser the bare metal will not support microbial growth. The dust would probably be normal household dust (human skin, paper dust and fibers from clothing) and nothing to worry about itself unless it becomes wet.

The second possible source of musty odors from the air handling unit is the condensate pan and coils. Frequently the condensate pan in an air conditioning unit becomes plugged if not cleaned on a regular basis. A plugged condensate pan can overflow. This may lead to the interior insulation of the air handler becoming wet and supporting microbial growth. If growth becomes established on fiberglass insulation, a musty odor can result. This happens frequently and when it does replacing the insulation may be required (a closed cell foam insulation is hydrophobic and doesn’t absorb moisture). Having a good filter that is properly installed and routine maintenance that includes cleaning the condensate pan and coils should prevent condensate moisture from becoming a problem.

If a plugged condensate pan in the air conditioning unit has overflowed onto the floor and gypsum board walls have become wet and moldy then replacing the water damaged gypsum board may be required. The floor itself may need cleaning/disinfecting and if carpet/particle board is below the unit then it may need replacing.

I am assuming there is no extensive duct work involved from your question. If that is not correct and the ductwork is rigid then duct cleanliness may be an issue as well.

In summary the odor may be prevented by simply cleaning the supply diffuser or it may be more involved and require remediation. Effective and routine maintenance usually prevents most of the problems associated with air conditioning systems.

Mark Goldman, CMC
Senior Air Quality Scientist
EFI Global, Inc.

This question was answered by Mary Biagiotti, a certified industrial hygienist with EFI Global.

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