How often should you seal air ducts?
Updated July 2026
Seal your ductwork once, thoroughly, then re-inspect the seals every 10 years or after any renovation that touches a duct run. Done right with brush-on mastic or a professional Aeroseal treatment, a seal lasts for decades, unlike cloth "duct tape," which dries out and peels within a few years. It matters because the U.S. Department of Energy estimates a typical home loses 20 to 30 percent of the air moving through its ducts to leaks into attics and crawlspaces. DIY mastic is $50 to $100 in materials; Aeroseal runs $1,500 to $3,000.
What changes the interval
| Your situation | Interval | Why |
|---|---|---|
| Never sealed, older home | Seal now | The DOE pegs typical duct loss at 20–30% |
| Accessible ducts in attic, crawlspace, or basement | DIY mastic | Brush-on mastic plus mesh tape, $50–100 in materials |
| Buried or wall-cavity ducts | Aeroseal (pro) | Injected aerosol seals from the inside, $1,500–3,000 |
| After adding a room or moving a run | Reseal the joints | New connections are the first place to leak |
| Old foil tape peeling or cloth tape used | Redo with mastic | Cloth "duct tape" fails within a few years |
The cost of skipping it
What skipping it costs: unsealed ducts leak 20 to 30 percent of your heated and cooled air into spaces you never occupy, so you pay to condition the attic. The symptoms are rooms that never reach setpoint, a system that runs nonstop, and dust and humidity pulled in through the return-side leaks. Sealing pays back through lower bills every month; run your own numbers on the cost calculator. It also pairs naturally with a periodic duct cleaning.
How to do it (A weekend · DIY mastic, or $1,500–3,000 for Aeroseal)
- Run the blower and feel along accessible duct joints for escaping air; a stick of incense makes the leaks visible as the smoke bends.
- Wipe each joint clean, then brush water-based mastic over every seam and screw, embedding fiberglass mesh tape on gaps wider than about an eighth of an inch.
- Seal where duct boots meet floors, walls, and ceilings, a spot that leaks in almost every house.
- Do not skip the return side; leaky returns pull attic and crawlspace air, dust, and humidity into the system.
- Seal the plenum and the joints at the air handler last, then let the mastic cure before running the system hard.
- For buried or wall-cavity ducts you cannot reach, price a professional Aeroseal job, and pair the work with a duct inspection: how often to inspect ductwork.
Knowing the interval is the easy half. OnOtto reminds you at the right interval, and it won't let you snooze it into next year. Tasks persist until they're done, and completing duct sealing schedules the next one automatically.
Put this on autopilot, free for 30 daysFrequently asked questions
Is Aeroseal worth it over DIY mastic?
It depends on access. If your ducts run through an open basement or reachable attic, DIY mastic seals them for $50 to $100 in materials and a weekend of work. Aeroseal, which injects an aerosol sealant that plugs leaks from the inside, shines when ducts are buried in walls, floors, or chases you simply cannot brush. It runs $1,500 to $3,000 but reaches leaks no hand can get to.
Can I just use duct tape to seal ducts?
No, despite the name. Cloth-backed "duct tape" dries out, the adhesive lets go, and it peels off within a few years, especially on hot supply runs. Use water-based mastic, brushed over seams with mesh tape on wider gaps, or a foil-backed tape rated to the UL 181 standard for ducts. Mastic is the gold standard: it stays flexible, fills irregular gaps, and lasts for decades.
How much will duct sealing lower my bills?
Because leaky ducts lose 20 to 30 percent of the air they carry, sealing a genuinely leaky system can trim a similar slice off the heating and cooling portion of your bill, though results vary with how bad the leaks were. Beyond the dollars you get rooms that finally hold temperature and less dust. Plug your figures into the cost calculator to estimate your own payback.
Do I need to seal ducts if I just had them cleaned?
They are different jobs. Cleaning removes dust and debris from inside the ducts; sealing closes the gaps where air escapes. A cleaning does nothing for leakage, and sealing does nothing for dust. If you are already paying for access to the ductwork, it is efficient to check for leaks at the same time: how often to inspect ductwork.