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Ductwork replacement and sealing in Los Angeles
In Los Angeles, duct repair and sealing is published at $800–$4,500 and new ductwork at $3,500–$8,000 in 2026. It usually comes up because a new AC or heat pump triggers California's duct leakage test, which old attic ducts often fail.
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At a glance
Why duct work shows up on an AC quote
The California Energy Commission says replacing or altering an HVAC unit needs a permit, the contractor seals and tests the ducts, and a third-party rater verifies the work, including duct leakage.
That test is where many Los Angeles change-outs gain a duct line: ducts in hot attics, many of them decades old, leak at joints, boots and the plenum.
Signs your ducts are the problem
| What you notice | What it often points to |
|---|---|
| One or two rooms never cool | Long or undersized runs, a disconnected boot, closed dampers |
| Dust that returns fast after cleaning | Leaks on the return side pulling attic air |
| System runs nonstop on hot days | Leaky ducts, undersized equipment, or both |
| Crushed or sagging flex duct in the attic | Restricted airflow; often replace rather than seal |
More causes and fixes: hot and cold spots after an AC installation.
What the leakage test checks
Under Title 24 Part 6, replacing the condensing unit, air handler or coil is an alteration that triggers duct sealing. Adding more than 25 feet of new duct means the whole system must test at 10 percent leakage or less. Refrigerant charge checks apply to heat pumps everywhere and to ACs in zones 2 and 8–15.
From 1 January 2026 the CEC's Energy Code Compliance (ECC) program took over field verification from the HERS program, so the third-party rater on a 2026 change-out works under ECC.
The rater's result is what lets the permit close.
Duct work cost in Los Angeles
| Duct repair and sealing Reliable H&A, Cold Cloud, E & A Mechanical | $800–$4,500 |
| New or fully replaced ductwork Reliable H&A, Cold Cloud, HVACProjectCost | $3,500–$8,000 |
| Full system with all-new ducts HVACProjectCost | $14,000–$22,000 |
| Asbestos abatement on old ducts Reliable H&A; least settled | $2,000–$9,000 |
Published LA ranges; none are our prices. Sources and dates: cost guide.
How the duct test fits into an AC job
- Pre-test or inspection of the existing ducts during the quote visit, if the contractor offers it.
- Equipment swap under the permit.
- Seal and test. The contractor seals joints, boots and the plenum, then measures leakage.
- Repair if it fails, then retest.
- Third-party verification under the CEC's ECC program.
- Permit closes once the rater's result and the inspection are in.
Get the duct line priced up front
A quote that says "duct sealing if required, billed after test" leaves the biggest variable open. Ask for a pre-test, or a not-to-exceed price for sealing, before you sign.
How ducts are sealed
| Method | What it is | Good for |
|---|---|---|
| Mastic | A paste brushed over joints and seams | Accessible joints, boots and the plenum |
| Foil tape (UL-listed) | Rated tape for duct seams | Seams on metal duct; cloth "duct tape" fails over time |
| Aerosol sealing | Sealant blown through the ducts from inside | Leaks in runs that cannot be reached |
| Replace sections | New duct where it is crushed or disconnected | Damage that sealing cannot fix |
Ask which method the contractor plans and why; the leakage test result after sealing is what counts.
Repair or replace the ducts?
Seal and repair
Keeps the layout; fixes leaks at joints, boots and the plenum. Published at $800–$4,500 (Reliable H&A, Cold Cloud, E & A Mechanical).
Replace
For crushed, disconnected, undersized or asbestos-wrapped ducts. Published at $3,500–$8,000 (Reliable H&A, Cold Cloud, HVACProjectCost).
Sealing fixes leaks at joints and connections and keeps the existing layout. Replacement makes sense when ducts are crushed, disconnected, badly undersized for the new system, or wrapped in material that needs abatement anyway.
New duct runs over 25 feet also bring the whole-system leakage limit into play. HyreHVAC's duct sizing calculator explains how size relates to airflow.
What to ask
- Have you tested the existing ducts, and what was the leakage result?
- Is sealing to pass the test included in the price, or quoted if needed?
- How many feet of new duct, and does that trigger the whole-system test?
- Who books the third-party rater?
- If asbestos is suspected, who tests it and who abates it?
- Will the new ducts be sized for the new system's airflow?
What duct work adds to a full system price: central air installation cost in Los Angeles.
Sources
- Reliable Heating and Air (Woodland Hills), AC installation cost in LA and Ventura County (retrieved 2026-09-29)
- Cold Cloud (Glendale), central air cost in Los Angeles (retrieved 2026-09-29)
- E & A Mechanical (Tujunga), heat pump installation cost in Los Angeles (retrieved 2026-09-29)
- HVACProjectCost.com, Los Angeles HVAC replacement cost (retrieved 2026-09-29)
- Energy Code Ace (CEC-supported), Single-Family Compliance Manual ch. 9, § 150.2(b)1E–F, 2022 code text; confirm against the 2025 code in force since 1 January 2026 (retrieved 2026-09-29) — verify before relying on it
- California Energy Commission, "Home Energy Rating System (HERS) Program" (retrieved 2026-09-29)
- California Energy Commission, "Building Energy Efficiency Resources for Single Family Homes" (retrieved 2026-09-29)
Questions
How much does duct replacement cost in Los Angeles?
LA sources publish new or fully replaced ductwork at $3,500–$8,000, and duct repair and sealing at $800–$4,500, in 2026. A whole system with all-new ducts is published at $14,000–$22,000.
Why does a new AC trigger duct work?
Because California's energy code treats replacing the outdoor unit, coil or air handler as an alteration that requires the ducts to be sealed and tested. Old ducts that fail the leakage test must be repaired before the permit closes.
What are the signs my ducts are leaking?
Rooms at the end of long runs that never cool, a dusty house, high bills for the comfort you get, visible gaps or crushed flex duct in the attic, and a system that runs nonstop on hot days. Only a leakage test measures it.
Who performs the duct leakage test?
The installing contractor seals and tests the ducts, and a third-party rater verifies the result. From 1 January 2026 that rater works under the California Energy Commission's Energy Code Compliance program, which replaced HERS for code verification.
Are old LA ducts likely to contain asbestos?
Some older duct wrap and joint tape did, and Reliable Heating and Air lists abatement as a separate adder. Do not cut or disturb suspect material yourself; ask for testing before work starts, and get any abatement scoped and priced in writing.
Flex duct or sheet metal?
Both are used in LA attics. Flex is quicker to run but loses airflow if it is kinked, crushed or too long; sheet metal costs more to install. What matters most is correct size, short straight runs and sealed joints, which the leakage test checks.
How much do leaky ducts cost me?
We have no LA-measured figure for that and will not print a generic one. Leakage means cooled air is lost to the attic, so the system runs longer for the same comfort. The leakage test gives your own number.
Should ducts be cleaned when the AC is replaced?
Cleaning and sealing are different jobs. Sealing is what the Title 24 test checks; cleaning is optional and helps mainly where ducts are visibly dirty or after construction dust. Do not let a cleaning line replace the sealing line on a quote.
Can I seal ducts without replacing the AC?
Yes, duct sealing can be done on its own and may improve comfort in rooms that never cool. The Title 24 test requirement, though, is triggered by the equipment change-out, not by sealing alone.
Next step
Free quote request
Get a quote to check against these numbers
- Tell us about the job. Service, ZIP, property and timing. The form says right away if your ZIP is outside the area.
- We check the license first. Requests go only to contractors whose CSLB C-20 license we have matched on the state register. If none covers your ZIP yet, we email you and say so.
- Compare what comes back. Line the written quote up against the published ranges and the quote checklist.
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