You've got the thermostat set to 72°F, but one room stays warm no matter what. Meanwhile, your energy bill keeps climbing. Before you assume your AC unit is failing, check something simpler: your ductwork might be leaking.
Leaky ducts let cooled air escape into attics, crawl spaces, and wall cavities before it ever reaches your vents — meaning your system runs longer and harder to hit the same temperature. The fix is often a lot cheaper than a service call: sealing the leak at the source.
Why Your AC Bill Keeps Climbing (It Might Not Be the AC)
Ductwork runs through attics, basements, and crawl spaces — places that get hot, cold, and physically bumped over the years. Common causes of duct leaks include:
- Loose or separated joints where duct sections connect
- Cracked or torn seams, especially on flexible ducting
- Gaps around vent boots where ducts meet the ceiling or floor
- Old tape or mastic that's dried out and lost its seal
Even small gaps add up. A duct system with multiple small leaks can lose a meaningful share of conditioned air before it reaches your living space — air you're paying to cool but never actually feel.
Signs You Have a Leaking Duct
You don't need to open up every duct run to spot a problem. Watch for:
- Uneven temperatures between rooms, especially rooms farthest from the AC unit
- Higher-than-usual energy bills with no other explanation
- Weak airflow at certain vents compared to others
- Dust or debris streaks near duct joints or vent boots — a sign air (and dust) is escaping
- Musty smells or humidity near an attic or crawl space duct run
If you notice any of these, a quick visual inspection of accessible ductwork is worth ten minutes of your time.
How to Seal Duct Leaks with Extreme Tape™
For accessible metal duct joints, seams, and vent boot connections, here's how to seal a leak:
Step 1: Turn off the HVAC system. Working on cool, still ductwork is safer and easier than working around moving air.
Step 2: Clean the surface. Wipe away dust and debris from the joint or seam. Old cloth tape that's peeling should be removed first for the best bond.
Step 3: Cut and position the tape. Cut a strip that fully covers the gap or seam, overlapping solid duct surface by at least an inch on each side.
Step 4: Press firmly along the full length. Work from one end to the other, pressing out any air pockets as you go. The aluminum-backed layer and ExtremeSeal™ Technology adhesive create a tight seal against the metal duct surface.
Step 5: Check the seal. Once the system is running again, feel along the repaired area for escaping air. A properly sealed joint should feel smooth and cool to the touch, not blowing.
Where Ducts Leak Most Often
Focus your inspection on these common trouble spots:
- Duct joints and connections in the attic or basement
- Vent boots where ductwork meets the ceiling, wall, or floor register
- Flexible duct seams, especially where it connects to rigid metal sections
- Connections at the air handler or furnace itself
Is Tape the Right Fix for Every Duct Leak?
Tape works well for accessible, visible leaks at joints, seams, and vent boots on metal ductwork — the kind of repair you can reach and see clearly. For duct leaks that are buried deep inside walls, inside a major trunk line, or part of a larger system-wide leakage problem, it's worth having an HVAC technician assess the full duct system. Sealing what you can reach yourself is still a smart first step, and it often solves the exact spot causing the temperature imbalance or noise you've noticed.
Stop Paying to Cool the Attic
A leaking duct means you're paying to cool spaces you'll never actually feel. Sealing accessible joints and seams is a simple weekend fix that can even out room temperatures and take pressure off your AC system.
Seal your ductwork before the next bill. Get Extreme Tape™ →
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FAQ
Can Extreme Tape™ be used on metal AC ducts? Yes — the aluminum-backed butyl tape bonds well to metal duct joints, seams, and vent boot connections.
Will sealing my ducts actually lower my energy bill? Sealing leaks reduces the amount of conditioned air lost before it reaches your vents, which can help your system run more efficiently — though total savings depend on how much leakage you had to begin with.
Do I need to turn off my AC before sealing a duct? Yes, it's safer and easier to work on ductwork when the system isn't actively pushing air through it.
Can I use this on flexible ducting, not just metal? Extreme Tape™ bonds to a range of surfaces, but for flexible ducting seams, make sure the surface is clean and firmly press the tape to conform to the shape.
What if I can't find where the duct is leaking? Feel along accessible joints and seams with the system running — escaping air is usually noticeable to the touch. For leaks you can't locate or reach, an HVAC technician can pressure-test the full system.