How long does ductwork last?
Updated August 2026
Ductwork lasts 20–25 years on average, and well-sealed sheet-metal runs can push past 50. What ends a duct system is rarely the metal itself: it is leaks. The average home loses 20–30% of its heated and cooled air through gaps at the joints, per the U.S. Department of Energy, so a network can be structurally intact yet worth replacing because it has gone leaky, been crushed in a crawlspace, or grown mold from a moisture problem. A full re-duct runs $2,000–5,000 and up.
Lifespan by type and situation
| Type or situation | Typical lifespan | Why |
|---|---|---|
| Sheet-metal (galvanized) ducts | 30–50+ years | The most durable; sealed seams are what let them last |
| Flexible (flex) duct | 10–25 years | The insulation and inner liner degrade; kinks and sags choke airflow |
| Fiberboard duct | 15–25 years | The board erodes and can shed fibers or harbor mold once it gets wet |
| Ducts in a damp crawlspace | Cut 5–10 years | Condensation rusts metal and rots liners; mold is common |
| Crushed or disconnected runs | Fails early | A section knocked loose in an attic can waste air for years unseen |
| Sealed and insulated well | 40–50 years | Mastic-sealed joints and dry space reach the top of the range |
Signs yours is near the end
- Rooms that never reach the thermostat setting while others overheat
- Dust streaks on the ceiling or walls near supply registers, blown out of leaky joints
- Whistling or rushing air sounds at the ducts whenever the system runs
- Utility bills climbing while the furnace and AC still test fine
- Visible gaps, disconnected sections, or crushed flex duct in the attic or crawlspace
- A musty smell through the vents, a sign of moisture or mold in the runs
How to add years
Sealing is the maintenance that matters most, because leaks, not age, condemn most duct systems. Sealing the joints with mastic or foil-backed tape (never cloth duct tape, which dries out and falls off) recovers the 20–30% of air a leaky system throws away and keeps humid air out of the runs. An occasional inspection of the attic and crawlspace catches a crushed or disconnected section before it wastes a whole season of energy, and drier ducts simply do not corrode or grow mold. The full routine, including when a duct cleaning is actually worth it, is in the ductwork maintenance checklist.
What it costs to replace: plan on $2,000–5,000+ for a full re-duct. Replacing on your own schedule, before it fails, is almost always cheaper than the emergency version. The home maintenance cost calculator helps you set the money aside before it comes due.
OnOtto tracks your duct inspections age and service history, and warns you before end of life instead of after the flood.
Track your home's systems, free for 30 daysFrequently asked questions
How do I know if my ductwork needs replacing?
Watch for rooms that never reach temperature while the system runs constantly, dust blowing from registers, whistling at the joints, and bills climbing even though the furnace and AC test fine. In the attic or crawlspace, look for crushed flex duct, disconnected sections, rust, or a musty mold smell. Leaks and damage, not the age of the metal, are usually what justify a re-duct. If sealing and repairs cannot recover the airflow, or the ducts are moldy, replacement is the call.
Is duct cleaning the same as duct sealing?
No, and they solve different problems. Duct cleaning removes dust and debris from inside the runs, which matters mainly after a renovation, pest activity, or visible mold; on its own it does not routinely lower your bills. Duct sealing closes the gaps at the joints with mastic or foil-backed tape, and that is what recovers wasted air and cuts energy use. If you can only do one, seal. Cleaning is occasional and situational; the ductwork checklist spells out when each is worth it.
How much conditioned air do leaky ducts waste?
A lot. The U.S. Department of Energy estimates that a typical duct system loses 20 to 30 percent of the air moving through it to leaks, holes, and loose connections. That is air you paid to heat or cool, escaping into an attic or crawlspace instead of your rooms. It shows up as a furnace and AC that run longer than they should and a house that never feels evenly comfortable. Sealing the joints is the fix, and it often pays back quickly on the energy bill.
Should I replace ductwork when I replace my furnace or AC?
It is the best time to look. The ducts are already exposed, the installer is on site, and a new high-efficiency furnace or AC only delivers its rated savings if the ducts are not leaking a third of the air away. If your ducts are past 20 years, undersized for the new system, or visibly damaged, folding a re-duct or a thorough sealing into the job makes sense. If they are sealed metal in good shape, leave them and put the money elsewhere.