Sealing Metal Air Ducts: What You Need to Know

The demand for energy efficiency in buildings is on the rise, and the Department of Energy has identified sealing ducts as one of the most effective ways to reduce energy consumption in HVAC construction. Unsealed ducts can cause up to 30 percent of the system's airflow to escape, resulting in a 40 percent increase in fan energy. To meet current standards, all joints, except for the seams with spiral locking, must be sealed with the class A seal of the National Association of Sheet Metal and Air Conditioning Contractors. The need for buildings with low duct leaks, energy efficient heating, ventilation and air conditioning systems, and green HVAC buildings is only going to continue to grow.

A commercial building with LEED certification can increase its sales price by 10 to 13 percent and rental rates for office buildings by 2 to 17 percent. To meet these stringent leak requirements, sheet metal contractors must use the right materials and strategies to seal the ducts. The first step in meeting low leak requirements is to use a quality duct sealant. It should be flexible during application and remain flexible over time, have good adhesion to the metal, be easily spread or sprayed, and not contain fillers like clay that can negatively affect flexibility and adhesion.

A “spongy” duct sealant can cause thin areas of sealant where the bristles of the brush have sunk into the metal. In addition, it is important to use the right tool for the job. There are several manufacturers of duct sealants in the HVAC market and most of these manufacturers have different grades of sealants. Premium duct sealants are high in polymers (rubber for greater flexibility and glue for greater adhesion) and provide greater tolerance if the installer applies a sealant that is too thin.

For unconditioned buildings in Nordic climates, it may be necessary to seal them with a solvent-based duct sealant during the winter. The most common area of duct leaks is at sheet metal edges. Quality sealants can often overcome this issue, but there are limitations. Brushing the transmission block will almost certainly cause air leaks due to its sharp edge and large gap.

By following these tips, sheet metal contractors can ensure that their projects meet low leak requirements and avoid costly labor costs and project delays. With quality materials and strategies, contractors can ensure that their projects are energy efficient and meet LEED standards.

Joel Reid
Joel Reid

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