Air Duct Repair and Sealing
If rooms never cool and bills keep climbing, cleaning will not help — the air is going into your attic instead. Duct leakage in a typical Valley house runs twenty to thirty per cent, and it is fixable.
Air duct sealing starts at $299 and a full-system mastic seal of all accessible joints is from $599. Replacing a damaged flexible run is from $249 per run. Every job starts with a leakage assessment so you know what you are buying. Call Dans Hollywood Chimney & Air Duct Cleaning at (818) 536-7759.
Find and document every leak, credited against work
Mastic seal of accessible joints and takeoffs
Every accessible joint, plenum and cabinet seam
Per run — crushed, kinked or disintegrated
The highest-pressure, highest-value repair
Where the jacket is torn, compressed or gone
Repair Is a Different Problem From Cleaning
Duct cleaning removes what is inside the ducts. Duct repair fixes the ducts themselves, and they are genuinely different jobs with different symptoms. If your air is dusty, you want cleaning. If some rooms never get cool, your bills keep climbing, or the system runs constantly without getting there, cleaning will not help you — because the air is going somewhere other than where you want it.
In a typical Los Angeles house with ductwork in the attic, duct leakage is the single largest efficiency loss in the whole HVAC system, and it is routinely in the twenty to thirty per cent range. That means a fifth to nearly a third of the air you are paying to cool is being delivered into your attic instead of your rooms. Because it happens out of sight, in a space nobody enters, it gets paid for year after year without ever being diagnosed.
Our housing stock makes this worse than average. The post-war tract construction that fills the Valley used long attic trunk lines with branch takeoffs, assembled quickly and sealed with cloth duct tape — which has a service life of a few years, not seventy. Attic temperatures well over a hundred degrees then bake every joint and every section of flexible duct, so the adhesive fails, the tape falls away, and the connection opens. A remarkable number of Valley houses have supply branches that are simply disconnected and lying in the insulation.
The repairs themselves are not exotic. Sealing joints properly with mastic rather than tape, reconnecting and strapping branches, replacing crushed or disintegrated flexible runs, and insulating duct that is bare or has lost its wrap. None of it is glamorous and all of it pays for itself in a way that very little else in a house does. Call (818) 536-7759 for an assessment.
What We Actually Repair
These are the five findings that account for nearly all duct repair work in Los Angeles housing, in rough order of how often we encounter them.
Failed Joints and Disconnected Branches
The most common finding by a wide margin. Branch takeoffs and section joints that were sealed with cloth duct tape when the house was built, where the adhesive has since baked out in attic heat. The tape dries, curls and falls off, and the joint opens — or the branch separates entirely and ends up lying in the insulation, delivering your conditioned air directly into the attic. The repair is to reconnect, strap mechanically, and seal with mastic, which is a brushed-on compound that stays flexible and does not degrade with heat. Mastic is the correct material and tape is not, including the metallic-looking tapes.
Crushed, Kinked and Collapsed Flex Duct
Flexible duct is a wire helix with a plastic liner and an insulation jacket, and it is easily damaged. Something set down on it in the attic crushes it. A run installed with a tight bend kinks and stays kinked. An unsupported span sags into a U that collects condensate. In every case the cross-section is reduced and the airflow through that branch falls off sharply. We find a lot of this caused by other trades working in attics — roofers, solar installers, anyone running cable. The fix is to replace the damaged section and support it properly on hangers at the correct spacing.
Leaking Plenum and Air Handler Connections
The plenum is the box on the air handler that the trunk lines come off, and the connection between cabinet and plenum is under the highest pressure in the whole system — which makes it the most expensive place to have a leak. A gap here is losing air at the point of maximum pressure, and because it is right at the unit it also means the system can be pulling hot attic air directly into the supply stream. Sealing the plenum and the cabinet seams is frequently the single highest-value repair available on an older Valley system.
Missing or Degraded Insulation
A duct carrying fifty-five degree air through a hundred-and-twenty degree attic needs its insulation jacket intact, and on a house of a certain age that jacket is often torn, delaminated, compressed or simply gone. Uninsulated duct in a hot attic does not leak air but it loses the cooling before it arrives, which feels identical from inside the house. Re-wrapping or replacing jacketed duct is straightforward and it is cheap relative to what it recovers. We check jacket condition on every run as part of any duct assessment.
Aeroseal-Type Internal Sealing
Where leaks are numerous, small and distributed across runs that cannot all be physically reached, an internal aerosol sealing process can be the right answer. The system is pressurised with an aerosolised sealant that is carried to the leak points and deposits there, closing gaps from the inside. It is more expensive than hand-sealing and it is not a substitute for reconnecting a disconnected branch or replacing a crushed run. It is genuinely useful on an otherwise sound system with diffuse leakage, and we will tell you honestly whether yours is that system or not.
Signs Your Ducts Need Repair, Not Cleaning
These are symptoms of air going to the wrong place. If this is what you are experiencing, a duct cleaning will not change any of it.
How a Duct Repair Job Runs
The assessment comes first because the repair depends entirely on what is wrong, and the findings are frequently different from what the symptoms suggested.
Leakage assessment and attic survey
We survey the whole duct system in the attic or crawlspace, locate and photograph every leak, disconnection, crushed section and insulation failure, and measure airflow at the registers.
Written findings and priorities
You get the photographs and an itemised estimate with the repairs ranked by how much airflow each one recovers, so you can do the high-value items now and the rest later if you prefer.
Reconnect and mechanically fasten
Separated branches are reconnected and strapped mechanically. A connection that relies on adhesive alone will come apart again, so nothing is sealed before it is fastened.
Seal with mastic
All accessible joints, takeoffs, plenum connections and cabinet seams are sealed with brushed-on mastic, which stays flexible and does not degrade in attic heat the way tape does.
Replace, insulate and verify
Crushed or disintegrated runs are replaced and supported on correctly spaced hangers, insulation is re-wrapped where needed, and airflow is re-measured at every register so you can see the before and after figures.
Air Duct Repair and Sealing — Frequently Asked Questions
Where We Provide This Service
Stop Paying to Cool Your Attic
A leakage assessment that shows you every leak with photographs, mastic sealing rather than tape, and airflow measured before and after. Serving the San Fernando Valley and East LA from 6330 Camellia Ave, North Hollywood, CA 91606.
Air Duct and HVAC Cleaning by City
Dan covers the whole Valley and East LA — CSIA-certified, written estimate first.