Ductwork Repair & Replacement in Los Angeles, CA

The symptom and the cause

Your AC Runs. The Room Doesn't Cool. Here's Why.

Damaged ducts are one of the most common causes of poor AC performance in Los Angeles homes.

Your AC runs for 45 minutes. The bedroom gets to 76°F. Last summer it reached 72°F in 20 minutes. Nothing about the system changed. The ducts did.

Duct damage is invisible. It happens above your ceiling, inside your attic. You don't see a crack or a leak. You see a room that won't cool down, an electric bill that climbs every July, and an AC that runs longer than it used to just to hit the same temperature.

Mister Cool California diagnoses the actual failure before touching a single section of duct. You get a written scope of work, locations, damage type, and what we're doing about each one, before any work begins.

See why an AC stops cooling

Local conditions

Los Angeles Attics Are Hard on Flex Duct

LA's attic conditions push flex duct to failure faster than almost any other climate in the country.

Here's what most homeowners don't realize about flex duct in Southern California: your attic doesn't just get warm in summer. It gets extreme. Attic temperatures in the San Fernando Valley, South LA, and communities like Carson and Lakewood routinely exceed 130°F by early afternoon. Some unventilated attics push past 150°F during heat events.

That sustained heat breaks down the plastic inner liner, the collapsed flex duct liner, inside flex duct over time. The liner is the tube that actually carries conditioned air to your rooms. When it collapses inward, airflow to that register drops dramatically. This failure mode is sometimes misread as a refrigerant or blower issue during diagnosis.

Pest activity compounds the problem. Rodents moving through attic spaces tear duct connections loose at the duct boot, the metal fitting connecting a flex run to your supply register or trunk line. A disconnected joint at one boot means 100% of conditioned air for that room dumps directly into your attic.

After 15 to 20 years in a Los Angeles attic, duct systems across neighborhoods like Compton, Norwalk, and Gardena are hitting the end of their useful life. The symptoms show up in your living room. The cause is above your head.

See duct sealing and leak testing

From the field

What I Found in a Hawthorne Attic Last August

A single disconnected boot was costing one Hawthorne homeowner hundreds of dollars every cooling season.

From our lead field technician:

I got called to a home in Hawthorne, a 1,400-square-foot ranch built in the early 1960s. The homeowner had been running her AC every day for three summers and her back bedroom still wouldn't drop below 80°F.

I pulled attic access and went in around 9 a.m. The attic was already above 120°F. Within the first ten feet, I found it: a flex duct run serving the back bedroom had pulled clean off the duct boot at the trunk line. The connection had been secured with foil tape, not duct mastic sealant, and the tape had failed completely, probably within the first two summers after installation. The entire run, maybe 18 feet of flex duct, was just lying in the attic insulation, pumping conditioned air directly into that space.

The rest of the duct system was in reasonable shape. Two other connections needed re-sealing with mastic. Three short sections of flex had minor liner compression from being kinked around a rafter, we re-routed those.

Total scope: one full run replacement, three boot re-seals with mastic, and two re-routed sections. The back bedroom dropped to 72°F that afternoon. We didn't touch the AC system.

That's the value of actually going into the attic before making a recommendation.

Scope of work

Repair or Replace: Here's How the Decision Gets Made

Not every duct problem requires full replacement. The scope depends on what the inspection actually finds.

We get this question on almost every duct call. Here's the honest answer.

Partial duct replacement, swapping out only the damaged sections while keeping runs that pass inspection, is the right call when the overall duct layout is sound and damage is concentrated in specific areas. That's most of what we do.

Full duct replacement makes sense when the existing layout is poorly designed, when damage is distributed across too many runs to make targeted repairs cost-effective, or when the system's overall age and condition make it unlikely to hold up through another five summers in an LA attic.

After our attic inspection, you get a written scope. Every damaged section is identified by location. Every recommendation is explained. You decide what to move forward with. No pressure in either direction.

One compliance note: California Title 24 and local Los Angeles building requirements call for a HERS duct leakage test after significant duct work. We account for that in our scope, it's not a surprise cost that shows up at the end.

Read the Title 24 compliance guide

The project, step by step

Our Duct Repair & Replacement Process

Every duct repair follows a three-phase sequence: inspect, repair, verify.

1. 1

   Phase 1: Duct System Diagnostics

   We start in the attic. A technician accesses the attic space and physically walks every visible duct run. We look for duct disconnection, joints that have separated from the boot or collar, collapsed liner sections, torn insulation jackets, crushed elbows from improper installation, and foil tape that has failed at connections.

   We map what we find. Damaged sections are identified by location: which room they serve, where along the run the failure is, and what type of failure it is. This map becomes your written scope of work.

   For cases where the extent of leakage matters, like verifying attic duct losses before and after a full replacement, we use a duct blaster test. A duct blaster test is a pressurization test that measures total air leakage from the duct system. It gives a real number, not an estimate.

2. 2

   Phase 2: Repair & Replacement Work

   Disconnected boots get re-secured and re-clamped. All connections receive duct mastic sealant, applied by hand to the joint, allowed to set, and covered with mesh tape on larger gaps before a second coat. No foil tape on any repaired connection.

   Sections requiring replacement get new R-8 flex duct pulled tight and supported at the correct intervals. Collapsed liner sections can't be re-expanded, those runs are replaced, not patched.

   On full replacement projects, we re-route runs where the original layout was creating unnecessary static pressure: long, kinked, or undersized runs that were limiting airflow regardless of their physical condition.

3. 3

   Phase 3: Post-Work Verification

   Before we close attic access, every repaired or replaced connection gets a visual inspection. Mastic is checked for full coverage. Flex duct is checked for kinking or compression between supports.

   Where a HERS duct leakage test is required by local permit or California Title 24, we coordinate that test as part of the project close-out, not as a separate engagement the homeowner has to arrange.

See our ductwork installation

Service area

Communities We Serve Across Greater Los Angeles

Mister Cool California handles ductwork repair and replacement throughout the Greater LA area.

We serve Los Angeles, Long Beach, Carson, Compton, Gardena, Hawthorne, Downey, Norwalk, Lakewood, Torrance, Inglewood, Whittier, and surrounding communities. We also reach Anaheim, Santa Ana, and communities throughout the Inland Empire. If your home is in Greater Los Angeles, we cover it.

Your town

Check my town

• Los Angeles
• Long Beach
• Carson
• Compton
• Gardena
• Hawthorne
• Downey
• Norwalk
• Lakewood
• Torrance
• Inglewood
• Whittier
• Anaheim
• Santa Ana

Next step

Ready to Find Out What Your Ducts Are Actually Doing?

A duct inspection from Mister Cool California starts with the attic, not a guess.

Call us at (323) 770-7737 or email info@mistercoolcalifornia.com to schedule your duct system inspection. We'll tell you exactly what we find, explain every recommendation in plain language, and give you a written scope before any work begins. That's how it works. Every time.

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Frequently Asked Questions

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