If the insulation on your house’s HVAC ductwork has seen better days, consider replacing or upgrading it to improve energy efficiency and reduce your utility bills.

This is particularly true if the ductwork is in the attic, where the intense summer heat can make your air conditioner work overtime to cool your home. Insufficient insulation exposes ducts to temperature extremes that reduce HVAC system efficiency, making your unit work harder to maintain comfort.

When working with fiberglass insulation, always wear:

Gloves are a good idea, too, but it can be hard to do the delicate fitting and taping required while wearing them.

    Repairing Leaks in HVAC Ductwork

    Start by turning your heating or cooling system on and feeling along the ducts for air leaks. Pay particular attention to any joints or connections in the ductwork, and mark any air leaks. Then, turn off the furnace or attic air conditioner unit.

    Repairing ductwork leaks is crucial because leaks can account for 20% or more of energy loss from ductwork. Focus on significant leaks first, then address more minor leaks. Mark each leak clearly so you can return to it after turning off the HVAC system.

    Cover any air leaks with metallic foil tape made for sealing ductwork. Don’t use standard cloth duct tape on HVAC ductwork since the adhesive will not hold up to extreme temperatures.

    For an added layer of protection, apply duct mastic to the tape and duct. Duct mastic permanently seals leaks, so they will not reopen. Apply it to clean surfaces and let it dry completely. 

    Depending on how many air leaks you find,  cleaning your duct system after repairs are completed might be a good idea. If the ductwork system contains extensive damage, ask your HVAC professional if air duct replacement is better.

    Insulating HVAC Ductwork

    Properly insulating ductwork is one of the most effective ways to boost HVAC system efficiency. Insulation helps minimize costly energy losses before conditioned air reaches your living spaces. Below, we’ll cover recommended materials and proper installation techniques when insulating ducts.

    When insulating HVAC ductwork, use foil-faced fiberglass insulation with an R-6 or higher R-value — the foil facing blocks radiant heat transfer. Look for insulation rated by Underwriters Laboratories for HVAC systems.

    metal foil
    Image Credit: Canva

    Use the insulation manufacturer-recommended metallic foil duct tape to seal and hold the insulation in place. Make sure the insulation’s foil surface is dust-free before applying the tape. Peel the tape’s paper backing off as you apply it to prevent the tape from sticking to itself. If the old insulation is in poor condition, replace it with new insulation.

    Cut the insulation to width and length with a square and a sharp utility knife. Fit it snugly around the duct without compressing the fiberglass. Compression reduces the insulation’s R-value

    Apply small tape pieces across the insulation seam to hold it in place. Then seal the entire seam length with a long tape strip. Eliminate any insulation surface gaps, which let convection currents bypass the insulation.

    Carefully cut and fit the insulation where branch lines and registers come off the main trunk line. Make sure no gaps remain. Maintaining insulation continuity maintains thermal performance.

    Verify the foil facing on the HVAC ductwork insulation is sealed securely with tape, preventing moist outside air from penetrating the insulation and condensing on the ductwork. Condensation can cause mold growth and drips.

    So, Is Insulating HVAC Ductwork Worth It?

    Properly insulating your HVAC ductwork provides valuable energy efficiency benefits. It keeps treated air from losing heating or cooling before reaching rooms, allowing your HVAC system to operate more efficiently. Insulated ducts also prevent condensation from forming on and inside ducts. Insulating ductwork is doable as a DIY project if you have some HVAC experience.

    When weighing duct insulation costs, consider the cost-effectiveness of installing a new HVAC system appropriate to your home’s square footage. Replacing an aging, inefficient HVAC system and insulating the ductwork simultaneously is often the best approach.

    FAQs About Insulating HVAC Ductwork

    How much does it cost to insulate ductwork?

    The average cost to insulate ductwork ranges from $0.50 to $1.50 per square foot in labor plus $0.30 to $1.50 per square foot for insulation material. Total costs for a 2,000-square-foot home often range from $1,500 to $3,000.

    Should ductwork be insulated?

    Insulate any ductwork running through unconditioned spaces like attics, garages, or crawlspaces. Uninsulated ducts lose tremendous energy through duct wall heat transfer. Properly insulated ducts save energy and allow HVAC systems to operate more efficiently.

    How long does ductwork insulation last?

    Ductwork insulation lifespan varies based on installation quality, duct location, and insulation thickness. Generally, foil-faced fiberglass HVAC duct insulation lasts 10 to 15 years before needing replacement. Signs of deterioration include visible damage, condensation, and loose insulation.

    Can I use fiberglass to insulate ductwork?

    Yes, fiberglass makes excellent HVAC duct insulation. Look for foil-faced, flexible fiberglass duct insulation rated at R-6 or higher — the foil-facing blocks radiant heat transfer. Carefully seal insulation seams and joints.

    Is it better to insulate the inside or outside of ducts?

    Insulating the duct exterior prevents condensation from forming on the ductwork and typically holds up better over time than internal insulation frequently disturbed by airflow. Insulate ducts from the outside whenever feasible.

    Editorial Contributors
    avatar for Danny Lipford

    Danny Lipford


    Danny Lipford is a home improvement expert and television personality who started his remodeling business, Lipford Construction, at the age of 21 in Mobile, Alabama. He gained national recognition as the host of the nationally syndicated television show, Today's Homeowner with Danny Lipford, which started as a small cable show in Mobile. Danny's expertise in home improvement has also led him to be a contributor to popular magazines and websites and the go-to source for advice on everything related to the home. He has made over 200 national television appearances and served as the home improvement expert for CBS's The Early Show and The Weather Channel for over a decade. Danny is also the founder of 3 Echoes Content Studio, TodaysHomeowner.com, and Checking In With Chelsea, a décor and lifestyle blog.

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    photo of Lee Ann Merrill

    Lee Ann Merrill

    Chicago-based Lee Ann Merrill has decades of experience writing and editing across a wide range of technical and scientific subjects. Her love of DIY, gardening, and making led her to the realm of creating and honing quality content for homeowners. When she's not working on her craft, you can find her exploring her city by bike and plotting international adventures.

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