Seal leaky ducts

Why? Ducts carry air from your heating and AC systems to each room of your home. When ducts have leaks, they can lose up to 30% of heated or cooled air before it reaches living spaces. Just like opening the window while the heat or air conditioning is on, leaving your ducts in poor repair wastes energy and money.
Do it yourself:
  • Check for obvious holes throughout the duct system. Focus your repairs on ducts you can easily access, such as those in attics, basements, crawlspaces, and garages.
  • Seal duct joints and any leaks. Use mastic, a flexible sealant, to seal leaks and cracks, since it lasts longer than regular duct tape. For holes and gaps up to half an inch across, reinforce the mastic seal with fiberglass mesh tape. Larger gaps may need to be repaired with rigid material.
  • Insulate accessible ducts. This will help prevent air leakage. The U.S. Department of Energy provides a table to help you determine what type of insulation to use.
  • To learn more and get started, check out the Do It Yourself Guide to Sealing and Insulation with ENERGY STAR® brochure.


Good to know: There are many types of mastic you can choose from. Speak with a knowledgeable representative at your local home improvement store to be sure you choose a sealant that will work well for your home.

Professional option: Hire a reputable contractor to seal and insulate ducts that are hard to reach or especially leaky. A contractor should also inspect the entire system to ensure it is functioning optimally and conduct other repairs, like fixing damaged ducts and sealing registers.

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