Heating and cooling
Ductwork replacement cost
A 1,500 sq ft house is about 12 supply runs, a return and 52 ft of trunk, and replacing them in the attic with a metal trunk and flex branches is about $7,335 — $564 a run, which is the number that travels between houses better than any per-square-foot figure. New branches on the old trunk are $3,598; a new system where there was none, $8,327. And on most old systems the leak is the job: a test and mastic on every joint is $2,076, and it recovers most of the quarter of the air the ducts were losing. This counts the runs, prices the four jobs on them, and says which one the test will point to.
Written and edited by Pablo Ruiz Quintero
Last reviewed 2026-09-23 · Nothing you type leaves your browser
Ductwork replacement cost calculator
The house, the runs, and what is wrong with them
A duct system is a run to every room and a trunk to feed them, priced by the run. Most old ones leak a quarter of their air, and sealing is priced before replacing.
About 12 supply runs.
1 return.
Worth testing first.
Trunk, branches, boots and registers, out and new. For a system past its life, one with asbestos wrap, or one that was never sized for the equipment on it.
A rigid trunk from the air handler, with insulated flex branches off it to each register.
Hot in summer, cold in winter, and every leak dumps conditioned air into it.
The crew can get to the runs without opening anything.
An HVAC crew, by the run.
Used only to pick a regional labour rate. It stays in your browser.
Replace the whole system
$7,335
12 supplies, 1 return · $564 a run · $5 per sq ft of house · 43.4 h
Seal first, then replace what the test finds
A typical system this age leaks about 25 per cent of its air into the attic, and sealing recovers about three quarters of that for $2,076 against $7,335 to replace. Test first; replace the runs the test finds crushed or fallen off.
By the run, not the house
12 runs. 334 ft of duct.
One supply per 125 sq ft or so, a return per floor, and a trunk to feed them: 282 ft of branch and 52 ft of trunk here. Two houses of the same size with different room counts get quotes a third apart, and the run count is why.
Outside the envelope
Ducts in the attic lose every leak to the outside and need R-8 insulation by code. The same ducts inside the living space — soffits, between floors — need neither, which is the argument for putting them there when the house is open.
One system, four jobs
Seal it, replace the branches, replace everything, or build new.
What the crew charges for
- 282 ft of branch — 12 supplies, 1 return
A rigid trunk from the air handler, with insulated flex branches off it to each register. What most houses get: the trunk carries the volume without losing it, the branches are quick to run.$733 - 52 ft of trunk
Sheet metal from the plenum, sized down as the branches leave it.$676 - 12 boots and collars
The metal box at the end of each run that the register sits on, with a collar and a damper.$288 - Registers and return grilles
Adjustable supply registers, and returns sized to bring the air back.$261 - Supply and return plenums
The box on the air handler the trunk starts from, supply and return.$320 - Trunk insulation wrap
R-8 by code outside the envelope.$73 - Leakage test on the new system
A duct-blaster test: the system pressurised and its leakage measured in CFM at 25 pascals, against the 4 per 100 sq ft a new system must meet.$280 - 43.4 crew hours in the attic
Hot in summer, cold in winter, and every leak dumps conditioned air into it. An HVAC crew of two, priced by the run and the foot of trunk, with the location deciding how fast the runs go in.$4,344 - The old ducts out
Bagged flex and cut metal, out through the hatch.$160 - Mechanical permit
A new or replaced system is inspected, and tested where the code applies.$200
What it costs
National average. Replace the whole system: 12 supplies and 1 return for 1,500 sq ft, sheet-metal trunk, flex branches, in the attic, open access. Not included: the air handler or furnace, a zoning system, asbestos abatement on old wrap, or a Manual J to resize the equipment.
The equipment the ducts feed is on the central air page and the furnace page; the tonnage it should be — which the ducts are sized to — is on the BTU calculator.
Worth knowing
- 1,500 sq ft on 1 floor is about 12 supply runs — one register per 125 sq ft — and 1 return: 282 ft of branch and 52 ft of trunk. A duct system is that count, not the square footage, which is why two houses of the same size get quotes a third apart.
- Ducts in the attic are outside the house's envelope: every leak dumps conditioned air there, and the code wants them insulated to R-8. The $73 of wrap on the trunk is that. Ducts inside the conditioned space need neither, which is the argument for a soffit instead of an attic when the house is open.
On this page — 5 sections
By the run, not the house
The short version
- 1,500 sq ft is 12 runs and a trunk: $7,335 to replace. $564 a run.
- Seal first: $2,076 by hand, $2,920 by aerosol. Old systems leak a quarter of their air.
- The attic wants R-8 and loses every leak; the basement wants neither.
- Finished ceilings double it: $10,893 against $7,335.
A duct system is a run to every room and a trunk to feed them. Manual D sizes each run from its room’s airflow, and a house has about one register per 125 sq ft — so 1,500 sq ft is 12 supplies, a return, 282 ft of branch and 52 ft of trunk. That count is the price. Two houses of the same size with different room counts get quotes a third apart, and neither quote is wrong.
supplies ≈ floor area ÷ 125 · branch ft = supplies × 22 + returns × 18 · trunk ft ≈ 0.028 × floor area
- 125 sq ft
- one register's worth of room in an ordinary house
- 22 ft
- the average branch from trunk to boot
- trunk
- the long axis of the house, from the plenum
Worked through — 1,500 ÷ 125 = 12 supplies and 1 return: 282 ft of branch and 52 ft of trunk — 334 ft of duct, and $7,335 to replace it all in the attic.
| Metal trunk, flex branches | All sheet metal | |
|---|---|---|
| The material | $1,409 | $3,496 |
| Crew hours, attic | 43.4 | 59 |
| 1,500 sq ft, replaced | $7,335 | $10,982 |
| Lasts | 25 years | 40 years |
| All flex instead | $5,723 | — |
MaterialsEstimator, Ductwork installation, sealing and replacement price survey · checked 2026-09-23
The leak is the job
The EPA’s field figure is that typical ducts lose a fifth to a third of the air that goes through them — into the attic, the crawl space, the wall cavities — through joints that were taped with cloth tape twenty years ago and boots that were never sealed at all. On a system that is not crushed, chewed or past its life, sealing gets most of that back for a fraction of replacing: mastic and mesh brushed on every reachable joint, or an aerosol sealant blown through the pressurised system that sets at the leaks nobody can reach.
The test decides. A duct blaster pressurises the system and reads its leakage; the code’s line for a new system is 4 CFM per 100 sq ft, and an old one that reads twenty is sealed, tested again, and the runs the test finds fallen off are replaced. Replacing a system that only leaked is the dear way to seal it.
25%
Typical old-duct leakage
EPA field data
$2,076
Test and seal by hand
334 ft of joints
$2,920
Aerosol, from inside
Tested before and after
$7,335
Replace everything
When the test says so
International Code Council, IECC R403.3 — Ducts: insulation and leakage testing (2021) · checked 2026-09-23
Where the ducts are decides more than what they are
Ducts in the attic are outside the house: in summer they sit in 130-degree air, in winter in the cold, and every leak dumps conditioned air where nobody lives. The code wants them insulated to R-8 there and R-6 in a crawl, and the crew works on the joists or lying down. Ducts in a basement or in soffits inside the living space need no insulation and no test, their leaks stay in the house, and the work is upright. The same 12-run system is 7,335 in the attic, 7,878 in a crawl and 6,176 in a basement — and when a house is open for a remodel, moving the ducts inside is the change that pays every month after.
| 1,500 sq ft, 12 runs | Seal | New branches | Replace all | New system |
|---|---|---|---|---|
| Attic | $2,076 | $3,598 | $7,335 | $8,327 |
| Crawl space | $2,257 | $3,862 | $7,878 | $9,014 |
| Basement | $1,716 | $3,070 | $6,176 | $6,880 |
| Inside the living space | $1,956 | $3,422 | $6,900 | $7,796 |
Metal trunk and flex branches, open access. Finished ceilings add a hole and a patch at every run.
Air Conditioning Contractors of America, ACCA Manual D — Residential duct systems · checked 2026-09-23
Before the crew comes
On the list
- Walk the house and count the registers and the returns. That is the run count, and the price.
- Find where the ducts run — attic, crawl, basement, ceilings — and how the crew gets to them.
- The age of the system, and whether the old wrap on metal duct could be asbestos (pre-1980).
- A duct-blaster test before anything is decided. Under 25 years and not crushed, seal.
- The equipment it feeds: a system replaced without a Manual J is sized to the old guess.
- Ask how the flex will be hung: pulled tight, strapped every four feet, gentle bends.
- A test at the end, in the quote. A duct job that is not tested is a guess.
What goes wrong
01Replacing ducts that only leaked
A typical system loses a quarter of its air through joints. Replacing is $7,335; sealing gets most of it back for $2,076.
Instead — Test, seal, test again. Replace the runs the test finds broken.
02Cloth duct tape as sealing
It dries and lets go within two summers in an attic, and the system is back where it was.
Instead — Mastic and mesh at every joint, or aerosol from the inside.
03Flex draped over the joists
Every sag and kink throttles it; a long draped run delivers half the air it was sized for.
Instead — Pulled tight, strapped every four feet, gentle bends — or a metal trunk.
04Uninsulated ducts in the attic
R-8 by code, and without it the trunk is a radiator in 130-degree air all summer.
Instead — Insulated flex and wrapped metal: $73 on the trunk here.
05Pricing by the square foot
A duct system is a number of runs. Two houses of the same size can differ by a third in the count.
Instead — Count the registers: $564 a run is the number that travels.
06Undersized returns
The system can only push what it can pull. Starved returns are noisy, uneven rooms and a struggling blower.
Instead — A return per floor, sized to the equipment, and a look at the return before the supplies.
07New ducts on old equipment without a Manual J
The runs are sized to a guess made thirty years ago, and the new system is as uneven as the old.
Instead — A load calculation first — the BTU page — then the ducts sized to it.
08Opening finished ceilings for ducts alone
Every run is a hole and a patch: $10,893 against $7,335 with open access.
Instead — Do it when the ceilings are open for something else, or seal what is there and wait.
- 01Count the runsOne supply per register, a return per floor. About one supply per 125 sq ft in an ordinary house; the count is the price.
- 02Find where they runAttic, crawl space, basement or inside the ceilings. Attic and crawl need R-8 or R-6 insulation and lose every leak to outside.
- 03Test before decidingA duct-blaster test says what the system leaks. Under 25 years old and not crushed or chewed, sealing usually wins.
- 04Decide the jobSeal; new branches on the old trunk; replace everything; or a new system where there was none.
- 05Choose the materialFlex throughout is cheapest and kinks. A metal trunk with flex branches is the standard. All metal lasts the house.
- 06Price the accessOpen attic or basement, or drywall opened and patched at every run — which doubles a duct job in a finished house.
A duct system is sized from the equipment’s airflow, and the equipment from the house’s load — the BTU calculator is where that number comes from before a run is cut.
What the ducts are sized to- Supply run
- One duct from the trunk to one register in one room. A house has about one per 125 sq ft, and a duct job is priced by them.
- Return
- The duct that brings room air back to the air handler, through a large grille — one per floor, more in a big house. Undersized returns starve the system.
- Trunk
- The main duct from the plenum that the branches leave from, usually sheet metal, sized down as it goes.
- Plenum
- The box on the air handler the trunk starts from — one for supply, one for return.
- Flex duct
- Insulated plastic on a wire helix. Cheap and quick, and it delivers its rated air only when pulled tight and supported; every sag and kink throttles it.
- Boot
- The metal box at the end of a run that the register mounts on, with a collar for the duct and often a damper.
- Mastic
- A thick sealant brushed over every joint and seam, with mesh where the gap is wide. What sealing means; cloth duct tape is not it.
- Aerosol sealing
- A sticky mist blown through the pressurised system that sets at every leak from the inside — for joints inside walls nobody can reach. Tested before and after.
- Duct-blaster test
- The system pressurised to 25 pascals and its leakage measured in CFM. The code's line for a new system is 4 CFM per 100 sq ft; old ones often leak five times that.
- CFM25
- Cubic feet per minute of leakage at 25 pascals — the number a duct test reports.
- R-8
- The insulation the code requires on ducts in an attic, R-6 elsewhere outside the envelope, and none inside it.
- Manual D
- The ACCA design method that sizes each duct from its room's airflow and derates flex for every bend. The reason a system is not sized by square feet.
Common questions
- How much does it cost to replace ductwork?
- About $7,335 for a 1,500 sq ft single-storey house — 12 supply runs, 1 return and 52 ft of trunk in the attic, with a sheet-metal trunk and insulated flex branches, new boots and registers, a leakage test and the permit. That is $4.89 a square foot or $564 a run. All flex is $5,723; all sheet metal $10,982; a 2,500 sq ft two-storey $11,163; behind finished ceilings, $10,893.
- How much does ductwork cost per square foot?
- About $4.89 a square foot of house to replace a whole system in the attic, $2.4 for new branches on the old trunk, $1.38 to test and seal. But a duct system is a number of runs — one per register, about one per 125 sq ft — and a house with more rooms than average costs more per square foot than one with fewer. $564 a run is the number that travels.
- Should I seal my ducts or replace them?
- Test first. A typical old system leaks about 25 per cent of its air into the attic or crawl, and sealing — mastic by hand at $2,076, or aerosol from the inside at $2,920 — recovers most of it for a third of the $7,335 to replace. Replace when the flex is crushed, chewed or fallen off its boots, when the system is past 25 years, or when the old wrap is asbestos. A replace the whole system on a 30-year-old system is $7,335, and the calculator says so.
- How much does duct sealing cost?
- About $2,076 for 1,500 sq ft by hand — a $350 duct-blaster test, then mastic and mesh on 334 ft of joints, boots and seams the crew can reach — or about $2,920 for aerosol sealing blown through the system, which reaches the joints inside walls and comes with a before-and-after test. Yourself, mastic and a test are about $634. Cloth duct tape is not sealing; it falls off in two summers.
- How much does it cost to install ductwork where there is none?
- About $8,327 for a 1,500 sq ft house with an open attic — a trunk and a run to every room, cut through whatever is between the air handler and the registers — and $12,345 when the ceilings are finished and every run is a hole and a patch. A ductless mini-split system is the number to compare it against before a ceiling is opened.
- Flex duct or sheet metal?
- Flex throughout is the cheap job — $5,723 against $7,335 with a metal trunk — and it delivers its air only when pulled tight, supported every four feet and run with gentle bends; draped over the joists it delivers half. A metal trunk with flex branches is the standard and the sensible default. All sheet metal, $10,982, is quiet, smooth and lasts the house; worth it in a basement where every foot is reachable. Flexible duct throughout: 15 years; Sheet-metal trunk, flex branches: 25 years; Sheet metal throughout: 40 years.
- Does it matter where the ducts are?
- More than what they are made of. In the attic or a crawl space they are outside the house's envelope: every leak dumps conditioned air outside, the code wants R-8 or R-6 insulation on them, and the crew works on joists or lying down — $7,335 in the attic, $7,878 in a crawl. In a basement or inside the living space they need no insulation and no test, the losses stay indoors, and the work is upright: $6,176.
- How many ducts does a house need?
- A supply run to every room that is heated or cooled — about one register per 125 sq ft, so 12 for 1,500 sq ft and 20 for 2,500 — and a return per floor, sized to bring the air back. Manual D sizes each one from its room's airflow, not from the house's square footage, which is why the count and not the area is the price.
- Do I need a permit to replace ductwork?
- For a new or fully replaced system, usually: a mechanical permit, about $200, with an inspection and — where the energy code applies — a leakage test to 4 CFM per 100 sq ft. Sealing or replacing branches on an existing trunk usually needs none.
- Can I replace ductwork myself?
- The materials are about $2,831 for the 1,500 sq ft attic system, and about $634 for mastic and a test to seal what is there. The work is runs pulled tight and strapped every four feet, every joint mastic-sealed, boots screwed to the framing, and a test at the end — because a duct job that is not tested is a guess. Aerosol sealing is a contractor's machine.
- How long does ductwork last?
- Flex 15 years or so before the plastic goes brittle and the tape at the joints has let go; a metal trunk with flex branches 25; all sheet metal 40 and more. Past 25 years, a system is replaced rather than sealed, and pre-1980 metal duct may carry asbestos wrap that an abatement crew removes first.
- Why is my house so uneven, room to room?
- Usually the ducts. Undersized returns, a flex run kinked round a joist, a branch that fell off its boot in the attic years ago, a trunk that leaks a quarter of its air before the last register. A duct-blaster test and a look in the attic find it, and it is the cheapest thing on this page to fix.
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About the author
Pablo Ruiz Quintero — Editor
Editor of MaterialsEstimator. Decides which documents count as a source, what every default value is, and where the line sits between what the reader parses and what the engines compute.
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