Yes, that’s “ducts,” not “ducks.” Many homes, particularly newer homes, have forced hot air furnaces that use air ducts to distribute heat and conditioned air throughout the house. Only in very recent years have HVAC installers been made to seal air ducts as a building code requirement. As a result, leaky air ducts abound, and homeowners are paying for it. Besides the cost and waste of your heated or conditioned air leaking out of your ducts, comfort and safety issues are also a concern for homeowners because leaky ducts pull unwanted air from basements and attics.
The duct system in an unconditioned attic or basement is part of your home’s thermal boundary. So it should not only be sealed, but insulated as well to energy code standards, which is R-6 in the basement and R-8 in the attic. According to the U.S. EPA, sealing and insulating your ducts can increase the efficiency of your heating and cooling system by 20 percent to 30 percent. Comfort level can also be noticeably increased by maximizing air flow.
First, with the system turned on, check your ducts for air leaks at the seams where sections are connected; also look for obvious disconnections and holes. Where the duct boot connects to the floor should be sealed also. Any penetrations that go through the attic floor or through the floor to an unconditioned basement should be sealed with foam around the outside of the ducts.
Use only duct insulation that has foil and fiberglass on the inside. This will give you the best thermal boundary possible. Do not use foil-faced bubble-wrap. It will not provide an adequate R-value unless installed with an air-gap between the duct and the wrap, which is very hard to do.
If 100 percent of your ducts are inside the building thermal envelope (in heated and conditioned air space), then you are very lucky and you need only seal them without insulating them. You can have your ducts tested to see if they meet code as new home builders are required to do. Theatrical fog can be used to pinpoint duct leakage problems.
Ducts should be air-sealed with metal tape and/or duct sealants such as Mastic. Alternatively, there is a new approach available to the homeowner that involves spraying an aerosol sealant inside the ducts. This has shown to be quite effective and must be conducted by a professional with the proper equipment. Lastly, believe it or not, duct tape is not effective or recommended for sealing ducts — so do not use it.
Tim Gould is the director of Informed Energy Solutions, Inc., located in Amesbury. Contact him at 978-388-6349. On the web at www.InformedNRG.com.