Do You Have a Sick House? The Mold - Air Duct Connection

Mildew on the wall next to a window
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A sick house is a house with a serious air quality problem. An area can be described as "sick" mainly because people who reside inside it for an extended period can develop symptoms of illness such as headaches, watery eyes, nausea, skin disorders, and fatigue. The illness causing factors vary and can include a build-up of air pollutants from household products, building materials, formaldehyde, and/or respirable particles.

In humid climates, sick houses are usually houses with a serious moisture problem. Moisture also plays an important role in promoting the growth and spread of mold (mildew). Molds produce spores, tiny encased "seeds," that float in the air. When a home is severely contaminated, thousands of mold spores can be suspended in each cubic foot of air. When people are repeatedly exposed to mold spores, they can develop allergic symptoms.

1. How Air Conditioners Cause Mold Problems

Visible mildew and mold is easy to identify because of its discoloration and odor. Keeping humidity in a home low can help keep visible mildew from returning, but if mold spores get into the air conditioning system, they can settle in the air conditioning ductwork, along with dust and other contaminants, where you can’t see or smell them. This is a worst case scenario because duct systems in humid climates are incubators for microbial pollutants like mold and bacteria. With the alternating high and low humidity conditions that regularly occur in air conditioning ducts during normal AC use, mold will grow, produce spores, and spread throughout the house.

2. Soil Build-up in Air Ducts

Effective filtering is a huge part of keeping ducts clean. If you have pets, plants, or other unique factors at play in your home, consider upgrading to a newer kind of filter the next time you swap them out. Newer filters can now remove smaller particles, and more of them as compared with the older fiberglass filters.

By neglecting to clean or change your filters, the build-up of dust and dirt on air conditioning filters causes air to by-pass the filter and carry organic dirt and spores into the ducts.

Leaks around duct joints in attics can also introduce dust and spores.

3. Duct Moisture

person cleaning out vents with a vacuum

Moisture in air ducts is nearly unavoidable, as the air leaving the evaporator becomes saturated as part of the AC’s normal process. If you run your air conditioner for the majority of the year, this leaves little time for that saturation and moisture to actually dry up.

High moisture can cause any dirt present in the duct to become caked on and provide an environment for mold to grow. The best way to address this issue is to either use the air conditioner less frequently or to clean the ducts regularly to clear out any caked on dirt and moisture.

4. Cleaning Air Ductwork

There are many different methods for cleaning ductwork, but because air ducts are such complex, closed systems, it is often difficult to maneuver equipment through them to clean or even locate every specific patch of dirt or buildup.

Most methods involve the use of shop vacs and motorized brushes, and while a dedicated professional can remove a fair amount of dirt with these tools, it is time consuming and the worker is often limited by how far though the duct their equipment can snake. More expensive options clean using essentially the same principle, but with larger and more powerful equipment.

Depending on the service you employ for this part of your ductwork, they may even use fiber optic camera feeds to see what the distant interiors of the duct look like and may actually cut in to certain points to remove localized instances of dirt or other harmful build up.

Another key factor is that none of these methods address the deeper concerns about mildew, molds, bacteria that can be a problem in humid climates, especially in fiberglass lined ducts.

In such cases, even a biocide specifically made to kill the mold may not be able to be put to use, since the presence of the biocide in the ducts and air that people breathe would be questionable and potentially harmful.