Companies that manufacture duct products are very much aware of consumers’ IAQ worries. Ironically, one of those worries is that buildings have become much better insulated. While a “tight” building is great for reducing energy costs, it can lead to higher levels of pollutants and poor IAQ. Since damp ductwork is a perfect breeding ground for mold, preventing that growth with an antimicrobial agent on duct products makes sense.

Enhanced Protection

Lindab, Stamford, Conn., is one of several companies that manufacture antimicrobial duct products. “There is an increasing awareness of serious problems associated with bacteria, molds, fungi, and other destructive microbes in the HVAC industry. Lindab decided to take the lead in addressing this crisis and develop a cleaner duct system,” says Larry Sunshine, vice president of Marketing.

As a result, the company’s Spiro products are now available as Spiro+AgION. These round and flat-oval duct systems come with the AgION antimicrobial compound, which contains silver ions in a zeolite matrix. When it comes time to treating the steel, the silver zeolite powder is blended into an epoxy coating and applied to the steel coil using a continuous roll coating process. The coating is fully cured during this process, which is designed to eliminate VOC emissions.

“The steel used in the Spiro+AgION duct system is precoated using the AgION antimicrobial coating by AK Coatings. This allays any concerns over whether the duct system is completely coated and ensures an even and solid distribution of the antimicrobial compound,” says Sunshine.

The antimicrobial begins to work after coming in contact with moisture. The silver ions are slowly released from the antimicrobial compound to the surface of the treated duct. There are a few theories as to how silver ions suppress microbes; scientists believe it is either by destroying the microbe’s cell wall, interrupting the microbe’s RNA replication process, or blocking the microbe’s cellular respiration through oxidation.

A Spiro+AgION duct system can be used wherever ductwork is being installed. However, Sunshine would not recommend installing just sections of it, since a partial installation will not protect the full system and, therefore, defeats its purpose.

All Lindab’s Spiro duct products (including single- and double-wall spiral and flat-oval ductwork, silencer, registers, dampers, and drum louvers) are available with AgION antimicrobial protection.

Flexible Protection

Another manufacturer that has come up with antimicrobial protection for its ductwork is JP Lamborn. The company recently announced it is now manufacturing “AMBlue,” a flexible air duct specifically designed and engineered with enhanced antimicrobial protection. This product is offered nationwide from the company’s Fresno (Calif.), Denver, and Knoxville (Tenn.) facilities.

“Mold has been a rapidly growing concern for homeowners, insurance companies, and the building industry,” says Tom Guyett, engineering manager and technical support. “While solutions were out there for other parts of the HVAC system, we saw a void when it came to the flexible air ducts. AMBlue fills that void.”

AMBlue flexible air duct is constructed with an inner core of coextruded blue nylon film with antimicrobial properties integrated through the coextrusion process. Guyett stresses, “The antimicrobial protection is built into the inner core of our AMB ducts, not applied to it.”

There’s nothing else contractors need to know when designing or installing a system with AMBlue ducts; the products were designed to meet normal requirements of conventional flex duct installations. AMBlue is offered in 25-foot lengths, with R6 and R8 thermal values, and a metalized vapor barrier.

There are no special requirements to maintain the antimicrobial properties, although a thick dust coating could reduce its effectiveness. According to Guyett, cleaning the ducts will not harm the antimicrobial properties, though it is possible to physically damage the duct wall. If cleaning is required, he recommends hiring a bonded professional trained in cleaning flex duct.

Costs And Guarantees

Antimicrobial duct products cost more than conventional duct. Guyett notes that AMBlue is being marketed as a premium product.

“Because of its current proprietary position in the market, we anticipate contractors would increase their margins on this product versus conventional flex duct. The additional cost of AMBlue on a typical attic ducted new home is less than $100,” says Guyett.

Sunshine notes that by using antimicrobial ductwork, contractors will be able to use this as an effective way to set themselves apart.

“The AgION coating adds 25 percent on a materials basis only. Labor costs remain the same, if not lower. If you look at the total cost of the duct system, the additional cost may range between 5 to 10 percent depending on labor rates. Taking it one step further, if you view this added cost as a percentage of the entire construction project, it comes out to less than 1 percent,” says Sunshine.

And both types of antimicrobial duct systems are built to last, say the manufacturers. Guyett states that because the antimicrobials are integrated into the inner core itself, the longevity of the resistance protection should be significant. “In addition to normal Petri dish testing, we have completed weather meter testing simulating five-plus years of normal use without a significant reduction in the products’ mold-inhibiting properties.”

Sunshine states that salt spray, water soak, and humidity testing have indicated that the antimicrobial benefit of Spiro+AgION should be present as long as the epoxy coating remains on the steel. As for resistance, he says the antimicrobial coating is similar to that of automotive paint applications, so small scratches on the coating’s surface of up to 1/4-inch wide will not affect the product’s performance. Since a scratch-free surface is ideal, a coating repair kit is available.

Media coverage of mold problems is intense, so it can’t hurt to learn more about the antimicrobial products being offered by manufacturers.

Publication date: 09/29/2003