There are more than 100,000 known species of mold. Mold spores (seeds) are everywhere - indoors and outdoors, in our building materials, on our clothes, and in the air we breathe. Mold can't be avoided, but it is possible to minimize the potential for growth in air systems. Mold is a common allergen; it exacerbates asthma, and can cause infectious disease in some people, which is why protecting ductwork is so important.


The best bet for controlling mold is to carefully control the moisture in buildings.

Mold doesn't require standing water to grow. High humidity is moisture enough for mold spores to germinate. High relative humidity levels in air-handling units occur anytime outdoor air dew points are above the cooling coil discharge temperature (typically 61°F). Air discharged from the cooling coils under these conditions usually has a relative humidity level of 90 percent or higher. Provided food is present, this is all it takes for mold to grow in an air distribution system.

Condensation is another problem, occurring whenever air comes in contact with surfaces that are cooler than the dew point of the surrounding air. This makes cold ductwork a prime area for unwanted moisture. This moisture can condense into liquid at the wrong place and the wrong time, wetting building components such as ceiling tiles, drywall, and carpeting, and setting the stage for mold growth.


Proper insulation is the best way to avoid condensation in ductwork. However, if improperly installed or damaged, some types of insulation can provide a cozy breeding ground for mold.

Among solutions currently being offered involve the use of closed-cell, elastomeric foam. According to proponents of this approach, the foam won't absorb moisture. Its smooth surface also inhibits the accumulation of dirt that can serve as food for mold.

Properly installed and maintained, elastomeric foam is an effective deterrent to biological contamination, proponents said. Even if closed-cell foam duct lining gets dirty or wet, its smooth surface makes it easy to clean.


Recently, one closed-cell insulation manufacturer has added an extra layer of protection against mold growth on the insulation by incorporating antimicrobial technology into its insulating products for air ducts and mechanical systems. Armacell LLC now incorporates an Environmental Protection Agency-approved antimicrobial compound into the manufacturing process of all its AP Armaflex products. Independent lab tests have shown that this antimicrobial technology is effective at preventing mold and mildew growth on the insulation. Because the antimicrobial agent is incorporated throughout the product, protection lasts the lifetime of the insulation, the company said.

Proper insulation practices, along with good maintenance practice, are an owner's best defense.

Publication date: 10/02/2006