Leaky air ducts? Why 20–30% of your air may be escaping
A typical home loses 20 to 30% of the air it heats and cools through leaky, disconnected, or poorly sealed ducts, according to ENERGY STAR — and it shows up as high bills, uneven rooms, and dust. Here's how to spot the leaks, find them, and decide whether to seal, repair, or replace.
Leaky ducts are a common cause. Call (888) 810-2291 for a licensed local contractor to test and seal them.
What are the signs your ducts are leaking?
Three signs stand out, and they can each have other causes, so treat them as a reason to look rather than a diagnosis:
- High utility bills in both summer and winter — if you've set the thermostat to save energy but the bills stay high in both seasons, escaping conditioned air is a prime suspect.
- Rooms that are always hotter or colder — a leaking or disconnected branch never delivers a room its full share of air.
- Dust that keeps coming back — leaky returns pull dust in from the attic or crawlspace and spread it through the house; dusty return vents are a tell.
Weak airflow at the registers and a whistling sound near the ducts are secondary signs. Uneven cooling has other causes too — see AC running but not cooling.
How do you find duct leaks?
You can inspect the exposed ducts yourself: look for holes, gaps, and loose joints at the connection points in the attic, basement, or crawlspace, where most leaks happen, and feel for air escaping. A smoke pencil held along a duct twirls where air is leaking. Ducts hidden inside walls and ceilings need a professional duct-leakage test (a duct blaster) to pinpoint. One caution: attics can top 100°F in summer, so don't overheat yourself doing the inspection.
How do you fix leaky ducts — seal, repair, or replace?
There are three fixes, matched to how bad the ducts are — seal small leaks, repair deteriorated sections, or replace ducts that are badly damaged or the wrong size. One myth to clear first: despite the name, duct tape is the wrong material — it dries out and fails within a couple of years. Use mastic or foil-backed tape instead.
Seal the leaksDIY / PRO · $30–$3,000
Sealing is the first fix and the one you can often DIY on exposed ducts — brush mastic over the seam or hole about as thick as a nickel, or use foil-backed (UL-181) tape, then wrap the run with R-6 insulation. For ducts hidden inside walls and ceilings, Aeroseal pumps an aerosol sealant through the system that closes holes from the inside and can last decades. DIY supplies run $30–$100; whole-home Aeroseal is $1,500–$3,000 for most homes.
Repair damaged sectionsPRO · $200–$700
Ductwork that's torn, crushed, or come loose at a joint is beyond sealing and gets a targeted repair — a technician replaces the deteriorated run or reconnects the section. It's a few hundred dollars depending on how buried the ducts are.
Replace the ductworkPRO · $3,000–$8,000+
Badly deteriorated ducts, or ducts that were sized wrong for the system in the first place, need replacing rather than patching. A full replacement is a larger job — commonly $3,000–$8,000+ depending on the home's size and access — and is often bundled with a system replacement; see new ductwork cost and when to replace for the full breakdown. If the system is also aging, run the numbers on repair or replace.
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Which of these can you do yourself?
Sealing exposed ducts you can reach — with mastic and foil-backed tape — is a reasonable DIY project, and sealing the accessible runs alone can recover a meaningful share of the lost air. Anything hidden in walls or ceilings, any section repair or replacement, and Aeroseal are professional work. If your ducts are mostly hidden or you're not comfortable in the attic or crawlspace, that's the line where you call.
What does duct repair cost?
DIY sealing supplies run $30–$100; the professional fixes climb from there depending on the scope. Here's the ladder, national reported ranges verified across cost sources:
| Fix | Typical range |
|---|---|
| DIY sealing supplies (mastic, foil tape) | $30–$100 |
| Professional spot-sealing / section repair | $200–$700 |
| Whole-home Aeroseal | $1,500–$3,000 |
| Full duct replacement | $3,000–$8,000+ |
The visit fee for an assessment is on HVAC service call cost, and broader repair pricing on AC repair cost.
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Is it worth fixing leaky ducts?
Yes — sealing recovers much of that 20–30% of lost air, so it lowers your bills, evens out the hot-and-cold rooms, improves indoor air quality, and eases the strain that shortens an HVAC system's life. ENERGY STAR puts the efficiency gain from sealing around 20%. One clarification: duct sealing (stopping air loss) is a different job from duct cleaning (removing dust) — this page is about the leaks. A yearly tune-up is a good time to have the ducts looked at.
Frequently asked questions
How much air do leaky ducts waste?
A typical home loses 20 to 30% of the air it heats and cools through duct leaks, disconnected sections, and poor sealing, according to ENERGY STAR. That's air you paid to condition escaping into the attic or crawlspace.
Can I seal ducts myself?
Yes, for exposed ducts you can reach in the attic, basement, or crawlspace — brush on mastic or apply foil-backed tape at the leaks. Ducts hidden in walls and ceilings, and Aeroseal, are professional work.
Why shouldn't I use duct tape on ducts?
Despite the name, duct tape is the wrong material — it dries out, loses its grip, and fails within a few years. Use mastic or foil-backed (UL-181) tape instead, which hold up to the temperature swings.
What is Aeroseal?
Aeroseal is an aerosol sealant a contractor pumps through your duct system under pressure; it seals holes from the inside, reaching leaks you can't get to in walls and ceilings. Properly done, it can last decades.
How much does duct sealing cost?
DIY supplies to seal exposed ducts run $30 to $100. Professional whole-home Aeroseal typically runs $1,500 to $3,000, more for large or badly damaged systems.
Do leaky ducts make rooms uneven?
Yes — it's a common cause. When a duct branch leaks or comes loose, the room it feeds never gets its full share of conditioned air, so it stays hotter or colder than the rest of the house.
Is duct sealing the same as duct cleaning?
No. Sealing closes leaks to stop air loss and improve efficiency; cleaning removes dust and debris from inside the ducts. They solve different problems, though a contractor may do both.