According to Energy Star, around 20-30% of the conditioned air that flows through your air ducts gets lost due to holes, cracks, and gaps.

If you have air ducts located in unconditioned areas of the home, such as crawl spaces and attics, it becomes especially important to find and seal your duct leaks. You don’t want to be paying every month to heat and cool non-livable spaces in your home. That’s a lot of wasted money and energy.

Additionally, the more duct leaks you have, the more dirt, debris, and moisture gets sucked into the ductwork whenever the system is on. If the holes in your ventilation and duct system are big enough, pests can get in as well.

No matter what kind of ducts you have (flexible, rigid, ductboard, etc.), it’s important to seal them up for better efficiency, comfort, durability, and indoor air quality.

How to Inspect and Seal Air Duct Leaks

Since ducts are often hidden away in walls, ceilings, attics, and basements, finding and sealing air leaks can get extremely difficult. Even if you don’t have much ductwork and everything’s easily accessible, this is still an intensive, time-consuming DIY project.

Consider contacting a professional to fully seal all of your duct seams and connections.

Duct Sealing Materials
Cleaning rag
Dust mask
Eye protection
Old clothes
Grease pencil
Incense stick or thin piece of toilet paper
UL-181 approved mastic sealant or HVAC aluminum foil tape (NOT duct tape)

If you are going into the attic, make sure you wear the proper clothing and protection for your eyes, head, and knees.

Contact a professional if your air ducts are difficult or dangerous to access. Professional HVAC companies use duct sealing technology that seals all air duct leaks from the inside out. They can also add duct insulation afterwards for better performance.

Duct Sealing Steps
Test for Duct Leaks

You can test your home for duct leaks using a piece of lit incense or thin piece of toilet paper.

Simply hold the smoke or paper up to duct seams and connections while the HVAC fan setting is “on.” You can also use the incense stick/toilet paper trick to identify other air leaks in the home, such as windows, doors, basement, and attic air leaks.

If you see the paper or smoke getting sucked in or blown out the ducts, you have an air leak. While it’s a good idea to seal all your air duct connections and seams, focus on the biggest leaks first.

Mark the duct leak locations with a grease pencil.

Warning: Sometimes there is significant ductwork damage that requires the skills of a professional. If you notice any major problems with your ductwork, such as disconnected sections, mold, or damp spots, contact a licensed HVAC technician to repair the ductwork.

Clean and Dry the Area to Be Sealed

After you have identified the duct leaks, prepare the surface for mastic sealant or aluminum foil tape. Take your rag and clean the area so the mastic sealant or foil tape will stick better. Make sure the area is completely dry before proceeding.

Apply Mastic Sealant or Aluminum Foil Tape

After cleaning and drying the surface, you can apply the tape or sealant. Follow the manufacturer’s instructions to a T.

Do NOT apply sealant to duct insulation or sleeve. Apply directly on the duct itself.

If there are any gaps larger than ¼ inch, use fiberglass mesh tape and mastic.

And remember, do NOT use duct tape since it tends to peel and doesn’t last very long.

Consider a Ductless HVAC System

By removing the need for ductwork, you’ll never have to worry about things like duct sealing and cleaning. Learn about your ductless heating and cooling options.

Contact OnTime Service for expert duct cleaning, sealing, installation, and repair. Professional HVAC companies use duct sealing technology that seals all air duct leaks from the inside out. They can also add duct insulation afterwards for better performance.


OnTime Service provides home evaluations and professional indoor air quality solutions for your home, including duct cleaning and duct sealing.

Give us a call at 205-942-1405 or schedule service online.

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