Should you repair or replace your ductwork?
Updated August 2026
← Every repair-or-replace call
Seal and re-insulate leaky ducts for $1,000–3,000 in nearly every case; replace them for $3,000–8,000 only when they are crushed, moldy, asbestos-wrapped, or too small for the system. Ductwork rarely fails outright, it leaks, and the typical older home loses 20–30% of its conditioned air through gapped joints and torn insulation before it ever reaches a room. Sealing those leaks recovers 10–30% of that lost airflow, which is why the repair almost always wins unless the ducts are physically wrecked or the wrong size for the equipment.
The short version
The decision here is not the 50% rule, it is a physical inspection. Walk the accessible runs in the attic, basement, or crawlspace and look for disconnected boots, crushed flex, mastic-free joints, and sagging or missing insulation. If the ducts hold their shape and only leak, sealing with mastic and foil tape plus adding a return or two is $1,000–3,000 and buys back most of the lost airflow. Replacement, at $3,000–8,000 for an average home, is reserved for ducts that are collapsed, mold-lined, undersized for a new furnace or AC, or wrapped in asbestos-containing insulation that has to come out by an abatement pro. When in doubt, a duct-leakage test puts a number on it.
Your situation, decided
| Situation | Verdict | Why |
|---|---|---|
| Joints leaking but ducts intact | Repair | Mastic and foil tape seal for $1,000–3,000 and recover airflow |
| Some rooms starved for air, others fine | Repair | Usually a sealing and balancing fix, not a teardown |
| Flex duct crushed or kinked behind storage | Repair | Re-run the affected section, not the whole system |
| Ducts lined with mold after a moisture problem | Replace | Contaminated duct board and flex cannot be cleaned safely |
| Undersized ducts choking a new high-capacity system | Replace | Old runs cannot carry the airflow new equipment needs |
| Asbestos-wrapped ducts in an older home | Replace | Abatement and replacement, never a patch job |
What each path costs
Repairs typically run $1,000–3,000; a replacement is $3,000–8,000 installed. Sheet-metal ductwork can last 30–50 years; flex duct and its insulation degrade faster. The call is physical condition, not age: seal what leaks, replace what's crushed, contaminated, or undersized. Price your own number on the home maintenance cost calculator before you commit either way.
The repair-or-replace call is easy when you know the unit's age and service history. OnOtto keeps both, plus the maintenance that delays this decision for years.
Start your home's service log, freeFrequently asked questions
How much air am I really losing to duct leaks?
In a typical existing home, 20–30% of the air your furnace or AC moves escapes into attics, crawlspaces, and wall cavities before reaching a register. That is air you paid to heat or cool, dumped into unconditioned space. You feel it as rooms that never get comfortable, a system that runs constantly, and dust that reappears a day after cleaning. Sealing the accessible joints and boots typically recovers 10–30% of that airflow, and it is one of the highest-return fixes in the whole HVAC system.
Should I seal ducts myself or hire a pro?
Accessible runs in an unfinished basement or attic are a reasonable DIY job with duct mastic and UL-181 foil tape, never the cloth tape that dries out and falls off within a year or two. Brush mastic over every joint, seam, and boot connection you can reach. The catch is that most leakage hides in walls, chases, and buried runs a homeowner cannot get to, which is where a pro with an internal duct-sealing rig earns the $1,000–3,000. Do the easy 60% yourself, or pay for the whole job if the ducts are inaccessible.
Do I need my ducts cleaned or replaced?
They are different problems. Duct cleaning removes dust and debris and makes sense after a renovation, rodent infestation, or visible mold, but it does nothing for leaks or bad airflow. Sealing fixes leaks. Replacement fixes ducts that are physically failed. A contractor pushing a full replacement for a dusty system is overselling; ask for a duct inspection and a leakage test first, and match the fix to the actual defect rather than paying $3,000–8,000 to solve a $300 cleaning problem.
Will sealing my ducts lower my energy bill?
Usually, yes, and it is one of the few HVAC upgrades that pays back quickly. If your system loses a quarter of its air to leaks, plugging most of that means the furnace and AC run shorter cycles to hit the same temperature. Homeowners often see a meaningful drop in heating and cooling costs after a $1,000–3,000 sealing job, plus more even room temperatures and less dust. Pair it with adequate attic insulation for the biggest effect, and run the payback on the cost calculator.