Sealing Leaky Ducts: What You Use Is All-Important

In the typical home, approximately 20 percent of airflow is lost through holes, leaks and poor connections at duct seams. Sealing leaky ducts is not only a matter of saving energy, but duct leaks also affect indoor air quality and the comfort and health of the occupants.

Sealing leaky ducts

Your home’s duct system is a network located in the ceilings, floors and/or walls. They’re made of thin metal, fiberglass or other substances. Over time, duct seams fail, and leaks occur. Duct sealing is best performed by an HVAC professional. However, many folks feel comfortable making it a do-it-yourself project.

You will need the right materials for sealing leaky ducts. The tried-and-true materials that should be used are:

  • Mastic: Mastic sealant, a gooey substance, is the preferred method to seal ducts by many HVAC pros. Be prepared to get a little messy when applying this compound. If you choose to use mastic, it’s vital that you first mechanically secure the duct seam with sheet metal screws. Once secured, you may use a paintbrush or your hands to spread the mastic around the seam. Wear rubber gloves regardless of using a brush or your fingers.
  • Mesh: Leaks larger than one-eighth of an inch need to be reinforced using fiberglass or drywall mesh before applying mastic. If you’re sealing fiberglass insulation board, use fiberglass mesh for all seams.
  • Butyl: Foil-backed butyl tape is a reliable duct sealant for steel, fiber board and flex ducts. It’s heat resistant and long-lasting. If you have areas of flex ducts in your home, consider using butyl tape for those duct seams for easier application than mastic.
  • Mechanical fasteners: Joint collars, sheet metal screws and compression straps are commonly used for sealing duct seams, in conjunction with mastic and/or butyl tape. If you have square ducts, each side of the ducts needs a sheet metal screw. Round ducts require three to four screws. Flex duct seams require compression straps for the best seal.

If you’re sealing leaky ducts around your home and have questions, contact Beyer Boys today. We’ve served San Antonio area homeowners since 1990.

Our goal is to help educate our customers in the greater San Antonio, Texas area about energy and home comfort issues (specific to HVAC systems).