How to Repair Leaks in HVAC Ductwork

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Leaks in HVAC ducts allow air from your furnace or air conditioner to escape, wasting energy and raising heating and cooling costs.

To seal holes or tears in ductwork:

1. Locate leaks by turning on the HVAC fan and feeling for drafts that indicate escaping air.
2. Turn off the fan and apply special metallic foil tape made for repairing ducts over the hole or gap. Don’t use standard duct tape, since the adhesive will come loose over time.
3. Use a brush to apply duct mastic over the tape and joints to improve the seal.

Watch this video to find out more.

Further Information

• How to Find Leaks in Ductwork (article)
• Testing HVAC Ductwork for Leaks (video)
• How to Improve the Energy Efficiency of the Furnace (article)
• How to Repair Bent Air Conditioner Compressor Fins (video)
• How to Clean an AC Condensation Drain Line (video)

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Leaks in ductwork are often found where lines branch off or separate. With the furnace fan running, you can feel air escaping the duct. Once you’ve found the leak, use foil duct tape to cover the gap and seal the leak.

For an extra layer of protection, use a paint brush to apply a coat of duct mastic. This thick, sticky material will dry to form an airtight seal that will keep the air in those ducts where it belongs.