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How to Perform Duct Sealing


Sealing HVAC ductwork improves airflow, temperature control, and indoor air quality. In any home or building, ductwork issues can cause 30% or more of conditioned air to be lost, reducing energy efficiency. Even small pinhole leaks can increase energy costs. These can also lead to condensation that allows mold to grow. Duct sealing can resolve most sources of air duct leakage; we’ll now look at ways it can be done.

Unless your ductwork is severely damaged, undersized, corroded, or old, you can try these methods, especially for ducts in the attic, crawlspace, or garage:

Air Duct Sealing Tape

The duct tape found in hardware stores is often mistaken for tape that seals an air duct. It is not suited for duct sealing because of its poor adhesion and resistance to temperature fluctuations. Although a temporary fix, butyl duct tape and oriented polypropylene tape are durable enough to create a good seal. 

For the best results, apply the tape with the heat on, as it sticks best at room temperature. But still, it’s only temporary because air movement, changes in temperature, and condensation will eventually cause the tape to fail.

Mastic Sealant

Mastic sealant can be applied directly to gaps in ducts. The thick, pasty substance comes in buckets. Collect some of the non-toxic, flame-resistant goo with a paintbrush and apply it to a gap, seam, or connection point. Water-based sealants are easier to clean up. Nonetheless, mastic sealers are long-lasting and best suited for gaps smaller than ¼”. For larger gaps, combine the sealant with tape.

For an effective application, clean the surface to be sealed before applying the mastic. Make sure to cover all holes and seams, or your efforts will not have noticeable results. And always remember to protect yourself with gloves, a hat, and a face mask. A disposable long sleeve shirt is also recommended.

Foil Tape

Use continuous strips of foil tape to cover lengthwise seams on straight ductwork runs. For an elbow connection, apply tape and then mastic with a paintbrush to the joints. Measure the duct’s circumference (and add a couple of inches). Then cut a matching size of foil-faced fiberglass insulation and wrap it around the duct. Pinch the seam closed and secure the insulation with shorter strips of foil tape. Lastly, place a long strip of tape along the entire seam.

Spray Foam/Liquid Rubber Sealant

Duct sealing can be performed from the inside of air ducts. However, it usually requires a professional. A contractor will remove the supply and return register grills, and plug the openings with foam rubber and tape. The duct system is then pressurized with a fan. 

Next, a computer determines how much air is leaking and how much sealant to use. Using a specialized machine, the material is sprayed into the ductwork. The sealant can cover everything from tiny gaps to cracks to faulty connections.

Why Consult with a Contractor

Duct sealing isn’t always enough to stop ductwork leaks. If your HVAC ducts have too many leak points, are damaged, or were poorly installed, replacing them may be more cost-effective. A qualified professional can thoroughly inspect and test your ductwork to determine the best solution for you and provide an estimate. 

Call Monarch Home Services for Duct Sealing

We provide high-quality duct sealing services in the Bakersfield area. Our solutions can help if your AC doesn’t effectively regulate indoor temperatures, the air quality is poor, you notice unusual odors or any duct is visibly damaged. Aside from using the latest duct sealing technologies, we provide duct cleaning, ductwork replacement, and air filtration services. For help from NATE- and EPA-certified professionals, call (661) 215-6657 today.

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