Leaky Locations Joints between duct sections, at their connectio…
Leaky Locations Joints between duct sections, at their connection to the plenum, and the plenum itself are common leak locations—especially when runs are installed in tight spaces and required to weave around structural elements. Researchers at Lawrence Berkeley National Laboratory (LBNL) found that duct tape almost always peeled away as its glue degraded. Panduit straps (large zip ties) connecting flexible duct sections can become loose or tear a section to create and expose leaks.
Insulate the Spaces – Consider insulating the areas where ducts …
Insulate the Spaces – Consider insulating the areas where ducts run, such as “cathedralizing” the underside of an unfinished attic roof deck with an open-cell foam or lining the foundation with rigid foam panels. Doing so will reduce the temperature (and pressure) differences between conditioned and unconditioned spaces to lessen the potential for leaks, as well as moderate ambient heat (in the attic, especially) that might degrade duct tape at connection joints.
Harry Whitver
Block the Leaks – Among several methods, consider a pressurized …
Block the Leaks – Among several methods, consider a pressurized aerosol sealant. Block all return and supply-air registers, connect the machine to the plenum, and force vinyl acetate adhesive particles through the ducts. The particles naturally seek out leaks to escape, but instead adhere, build up, and cure at those locations until the gaps are sealed from the inside. The process costs an estimated $300 to $1,800 and purports to reduce duct leakage by up to 90 percent, assuming a good initial duct installation job.
Up to 30 percent of a home’s heating and cooling energy can be lost through leaks in the ducts of a forced-air system, especially in those located in unconditioned attics, crawlspaces, and basements.
Leaks can result from improper installation and occur within only a few months of occupancy, leading to homeowner complaints about high energy costs and poor indoor comfort well within a builder’s warranty service window.
The problem is two-fold: First, duct runs located in unconditioned spaces create pressure differences between the air temperature within and outside the duct that magnify and eventually exacerbate leaks and thermal loss through the ducts.
Duct connections are the other problem area. Whether old-school sheet metal or new-age flexible runs, the joints at the furnace plenum and between duct sections are ripe for leaks upon installation and over time.
The resulting air and thermal loss reduces the efficiency of the heating and/or cooling equipment (read: a four-ton unit may be reduced to a three-ton capacity), hindering its ability to maintain desired indoor temperatures and occupant comfort as designed and calculated on the spec sheet.
Commission a duct blast test just prior to occupancy to identify and seal leaks, and consider insulating areas where ducts run to reduce temperature and pressure differences.
