Duct Sealing, Leak Detection & Testing in Los Angeles, CA

What leaky ducts cost

Your Ducts Could Be Adding $40 to $80 to Your Monthly Bill

Most Los Angeles homes lose 20 to 30 percent of their conditioned air through leaky ducts.

That air never reaches your living room. It bleeds into the attic, the walls, or the space between floors. Your compressor runs longer to compensate. Your SoCal Edison bill climbs. And the rooms at the end of the longest duct runs never quite cool down. Duct sealing in Los Angeles fixes the actual source of the problem, not just the symptoms.

Local conditions

LA Attics Make Duct Leakage Worse Than Almost Anywhere Else

Los Angeles attic temperatures hit 130°F to 140°F during summer. That heat destroys duct connections over time.

Here's what most homeowners don't realize about flex duct in a hot attic: the liner physically contracts and expands with temperature swings. After years of that movement, the liner pulls back from the collar fitting at the duct boot, the metal connector where a flex duct meets a register grille or plenum box. A small gap opens. Conditioned air escapes directly into that 135°F attic space instead of your bedroom.

We see this consistently across the LA Basin. The San Fernando Valley sees the most severe attic heat. Long Beach, Carson, Alhambra, and the Pomona Valley all have the same problem with aging flex duct systems. The climate accelerates failure in ways that cooler markets simply don't experience.

We cover the full stretch, from the Valley south to Long Beach, east through El Monte, San Gabriel, and Whittier, and west into Culver City and Santa Monica.

See our ductwork installation

From the field

What Our Lead Tech Found When He Pulled the Attic Hatch in Hawthorne

A routine high-bill call turned into a textbook duct leak case, and the homeowner's system was only nine years old.

From our lead HVAC tech:

I got a call from a homeowner in Hawthorne last summer. His Edison bill had jumped about $85 month-over-month. The AC was running fine, no refrigerant issues, no dirty coils, thermostat was accurate. On paper, nothing was wrong.

He assumed the system was getting old. It was nine years in, young enough that replacement made no sense. I told him I wanted to check the ductwork before we made any decisions.

I pulled the attic hatch and immediately saw the problem. Two flex duct runs had separated at the plenum, the central distribution box that connects the air handler to the branch ducts. The liner was still attached to the collar with a zip tie, but the actual duct material had pulled back about two inches. Both gaps were open to the attic.

I ran the duct blaster test, a pressurization device we attach to the duct system that measures airflow leakage in cubic feet per minute, or CFM. His system tested at 187 CFM of leakage. Acceptable leakage for a home his size runs under 60 CFM. He was losing more than three times that.

We sealed both plenum joints with mastic sealant, a thick, paste-based compound, and reinforced the boot connections on four registers that were pulling loose. Re-tested at 41 CFM. His next Edison bill dropped by $73.

That's a real number. Not an estimate. We had the test results to prove it.

Documentation

Your Written Test Results Are Worth Keeping After the Job Is Done

Before-and-after duct blaster results protect you at resale, at permit inspection, and during any future HVAC work.

When we complete a duct sealing job, we hand you both test reports, the pre-sealing leakage rate in CFM and the post-sealing result. That documentation matters beyond confirming the work was done.

California's Title 24 energy code requires a HERS duct leakage test, a certified Home Energy Rating System evaluation, on AC replacement installations. If your ducts have already been sealed and tested, that paperwork can simplify the compliance process when you eventually replace your air handler or condenser.

It also matters at resale. A buyer's home inspector may flag duct leakage. If you have a certified test showing your ducts are within acceptable limits, that conversation is already answered. You're not guessing. You have documentation.

Mister Cool California provides both reports in writing, every time.

Read the Title 24 guide

The visit, step by step

How the Duct Sealing Process Works

Three steps. Every job. No skipped phases.

1. 1

   We begin with a full duct blaster pressure test. The device attaches to your air handler and pressurizes the duct system. We measure the total CFM of air escaping the system and identify the zones where pressure drops fastest. This tells us exactly where leakage is concentrated, boots, plenum connections, flex duct collars, or return air pathways, before we touch anything.

   Leakage in LA homes clusters at three points most often: the plenum box, the duct boot connections at registers, and anywhere a flex duct run has been repaired or extended.

2. 2

   We work through each identified leak point. Mastic sealant goes on every boot connection and plenum joint. Larger gaps get mesh tape bedded in mastic for structural reinforcement. We skip duct tape, it degrades within two to four years in attic conditions. Every accessible section of ductwork gets a visual inspection for disconnected runs or crushed flex duct that restricts airflow.

3. 3

   Once sealing is complete, we run the duct blaster test a second time. The post-sealing CFM number confirms what the work actually achieved. We document both numbers on a written report. If the result doesn't meet the target leakage threshold, we keep working. You see the final number before we pack up.

Service area

Neighborhoods We Serve Across Los Angeles

Mister Cool California handles duct sealing and leak detection across the full LA Basin.

We serve Los Angeles, West Hollywood, Beverly Hills, Culver City, Santa Monica, Inglewood, Hawthorne, Burbank, Glendale, Pasadena, Alhambra, El Monte, San Gabriel, Monterey Park, Torrance, Gardena, Compton, Downey, Carson, Long Beach, Whittier, Redondo Beach, Lakewood, and surrounding communities. If you're in Greater Los Angeles, we cover your area.

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Frequently Asked Questions

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