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Hot upstairs, dusty air, high bills
Duct Repair, Sealing and Replacement in Los Angeles
If one end of the house never cools down, the problem is often not the AC. It is the ducts. In many Valley homes they run through an attic that can pass 130°F in summer, and leaks there dump cooled air into the attic before it reaches your bedrooms.
- Inspection first: we find the leaks, crushes and disconnects
- Repair, seal or replace, whichever actually fixes the problem
- Title 24 duct testing handled when it is required
Typical 2026 duct costs
- Minor leak sealing (1 to 3 leaks) $100 to $500
- Section replacement (10 to 30 ft) $300 to $1,500
- Whole-house repair and sealing $800 to $6,000
- New ductwork, LA install $5,000 to $8,000
Repair ranges: PickHVAC national data, May 2026 (coastal metros run higher). New ductwork: HVAC Project Cost, Los Angeles, July 2026.
The short answer
How Do I Know if My Ducts Are the Problem?
Suspect the ducts if the AC runs fine but some rooms stay hot, especially rooms at the end of long runs or on the second floor. Other signs:
- Weak airflow from some registers and strong airflow from others
- Dust building up quickly, or dust streaks around supply registers
- A musty or attic smell when the system starts
- Power bills that climbed even though the AC was serviced
- Rooms that are hot in summer and cold in winter
A duct leakage test measures exactly how much air is escaping. It turns guesswork into a number, and it is the same test California’s Title 24 code uses.
LA ducts
Why So Many LA Ducts Leak
- Hot attics. Valley ranch homes built from the 1950s to the 1970s usually have ducts in the attic. Decades of summer heat break down tape, connections and insulation.
- Crushed and kinked flex duct. Flex duct that was squeezed during a reroof, a solar install or someone walking the attic chokes airflow.
- Disconnected runs. A duct that has fallen off its boot blows conditioned air straight into the attic.
- Rodents. Roof rats chew through flex duct and its insulation.
- Old materials. Some ducts in pre-1980s homes were wrapped or taped with materials that contained asbestos. Do not cut or tear old duct wrap yourself; have it tested first.
- Additions. Rooms added later were often tapped off an existing duct that was never sized to feed them.
The fix
Repair, Seal or Replace?
| Situation | Usual fix | Typical range (2026) |
|---|---|---|
| A few leaks or a loose connection | Seal joints with mastic, reattach and strap runs | $100 to $500 |
| One crushed or torn run | Replace that section | $300 to $1,500 |
| Leaks throughout, ducts in decent shape | Whole-house sealing and repair | $800 to $6,000 |
| Old, undersized, damaged or uninsulated ducts | Full replacement, often with a new system | $5,000 to $8,000 in LA |
If you are replacing your AC anyway, check the ducts at the same time. A new high-efficiency system connected to leaky ducts still leaves you with hot rooms, and you will not get the efficiency you paid for. See AC installation.
Rules
Title 24 Duct Testing in Los Angeles
California’s Title 24 energy code calls for duct leakage testing in many situations, including most AC or furnace replacements and when large sections of ductwork are replaced. A third-party HERS rater verifies the result. In the City of LA, the work normally runs under an LADBS mechanical permit.
This matters for two reasons. First, it proves the ducts are actually sealed. Second, LADWP rebates require a final permit, and the permit cannot be finaled until the required tests pass.
Cleaning
Do I Need Duct Cleaning?
Most homes do not need routine duct cleaning. It is worth it when there is a clear reason:
- Soot or ash after a wildfire smoke event, especially near the Palisades and Eaton burn areas
- Visible mold growth inside the ducts or on the coil
- Rodent nesting or droppings in the ductwork
- Construction dust after a remodel
If you are mainly worried about smoke, start with filtration. Cleaning dirty ducts that still leak just pulls new dust in.
FAQ
Frequently Asked Questions
How much does duct repair cost in Los Angeles?
National 2026 data puts minor duct sealing at about $100 to $500, replacing a 10 to 30 foot section at $300 to $1,500, and whole-house repair and sealing at $800 to $6,000. LA prices usually sit toward the higher end. New ductwork for a whole home runs about $5,000 to $8,000 in LA.
Why is my upstairs so hot even with the AC on?
Usually leaky, crushed or undersized ducts in the attic, plus heat rising and a hot roof. A duct leakage test shows how much cooled air is escaping before it reaches the rooms.
Do I need a permit to replace ductwork in Los Angeles?
Large duct replacements generally fall under an LADBS mechanical permit in the City of LA, and Title 24 can require duct leakage testing by a HERS rater.
Is duct sealing worth it?
For leaky attic ducts, yes. Sealing keeps cooled air in the house, which improves comfort in far rooms and cuts wasted energy.
How often should ducts be cleaned?
Only when there is a reason, such as soot after a smoke event, mold, rodents or remodeling dust. Routine cleaning is not usually needed.
Related
Related Services and Guides
AC installation
Check the ducts before you buy a new system.
Indoor air quality
Smoke, ash and better filtration.
AC maintenance
Spot crushed or disconnected ducts early.
Ductless mini-splits
Cool hot rooms without new ducts.
Rooms that never cool down?
Call for a duct inspection. You get photos of what is wrong and a clear price to fix it.
Last updated October 2026. Prices are published 2026 Los Angeles market ranges, not quotes. Rules and rebates change, so check the official source before you buy.