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5 Effective Duct Sealing Methods


Leaky ductwork doesn’t only affect HVAC efficiency. It also allows unfiltered air into your home, leading to contamination by outside pollutants. Moisture issues and mold can result as well. At Waldrop, we provide duct sealing and repair services to resolve the problem.

Ducts must be properly sealed whether they’re in conditioned or unconditioned spaces. A leaky duct in your unfinished basement, attic, or crawlspace can allow cooled or heated air to escape and let particulates and volatile organic compounds in, no matter how well the rest of your home is sealed. 

But duct leakage issues can be stopped or prevented. These are some of the most effective duct sealing methods we recommend.

1. Foil Tape

Aluminum-based tape can be purchased at any hardware store. It’s rated for use on ducts, unlike cheaper plastic adhesive tape, and is easy to apply. Purchase tape that’s heat-rated and has the Underwriters Laboratory (UL) label. Foil tape is a temporary fix for duct leaks. It lasts a few years at most and eventually wears out, causing it to detach from the duct.

2. Mastic Tape

Mastic tape should be used throughout a duct system. Common leak points include the connections between ducts and plenums and air handler cabinets. To prevent leakage, seal these areas with mastic. Also, place it at all joints and seams. The tape should be about ⅛ inch thick for maximum effectiveness. When used properly, mastic tape can last 15 to 25 years.

If gaps are larger than ⅛ inch, first cover them with fiberglass mesh tape. Then apply mastic tape. Before sealing flexible ducts with mastic tape, connect all components and fasten the inner liner using a nylon draw band. It’s best to use a manufacturer-approved tool to do this.

3. Mastic + Latex Duct Sealant

A fiber-reinforced latex duct sealant is strong and durable. The water-based, paste-like material is easily applied to a leak with a paintbrush and will harden thereafter (mastic duct sealant can also be applied using a caulk gun). A leak that’s larger than ¼ inch wide should be fixed. But if you can, push loose sections of duct together and fasten them with sheet metal screws. Otherwise, the gap can be covered with foil duct tape. 

4. Insulate Ducts

Ducts in unconditioned areas should be insulated with a vapor barrier. It prevents heat gain or heat loss through the wall of the duct. It also prevents condensation from forming on the outside, which can lead to water damage and mold. The insulation should completely cover each duct; use UL-181 tape to seal the seams in the insulation. Make sure all gaps and voids are covered.

5. Aeroseal

Larger duct leaks should be sealed by a licensed professional. Aeroseal is a duct sealing method that doesn’t require breaking down walls or ceilings or accessing ducts in hard-to-reach places. A technician can test for and identify leaks by blocking all vents and using a computer to find them.

Instead of applying a sealant directly to the point of leakage, a material is blown into the ductwork and seals leaks in the supply and return chambers, boots, elbows, and connecting fittings. Registers are removed and openings are plugged to prevent the sealant from circulating in your home.

Call Waldrop to Schedule Duct Sealing Services

Our NATE-certified technicians ensure HVAC ductwork is efficient, from proper design and installation to duct sealing and repair. Our team can determine when to repair or replace ductwork. We’re available throughout the Greenville and Spartanburg area. For duct sealing, air conditioning, and other home services, call Waldrop at (864) 536-0887 today.

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Greenville, SC

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Had the best experience with Waldrop, we will forever be in their debt. Not only the most professional group of men but the most honest, stand by your word company! I would recommend Waldrop to

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