Duct Repair and Sealing in San Jose & the Bay Area: Fix Damaged Ducts and Hidden Leaks Together
If a duct has come apart in your attic, been crushed in the crawl space or chewed by rodents, the air meant for one of your rooms is going somewhere else. Some of that damage you can see. Much of the leakage in a typical system is hidden in joints and seams you can't reach. MaxSeal repairs damaged ducts by hand, starting at $450, and seals the hidden leaks with Aeroseal, so you fix the whole system in one visit instead of patching what's easy to find.
Key Takeaways
| Common Question | Short Answer |
|---|---|
| How much does duct repair cost? | MaxSeal's manual duct repair starts at $450. Aeroseal sealing for the hidden leaks is $3,000–$3,500 per system if you need it. See our price list |
| What kinds of duct damage need hand repair? | Disconnected runs, crushed or kinked flex duct, torn sections, rodent damage and any gap larger than about 5/8 inch. How we repair ducts |
| Can Aeroseal fix a disconnected duct? | No. Aeroseal seals holes up to about 5/8 inch from the inside. Larger gaps and disconnected ducts are repaired by hand first. How it works |
| Why not just repair the leaks I can see? | Many leaks are inside walls, floors and boots where no one can reach them. Hand repair handles the big damage and Aeroseal seals the rest. Compare the options |
| How do I know my ducts need repair? | Rooms that get little or no air, a dusty house, high bills or visible damage in the attic or crawl space. A test confirms it. About the leakage test |
| Should I replace my ducts instead? | Often not. If the ducts are mostly sound, repair and sealing typically costs much less than replacement. Aeroseal vs manual vs replacement |
| Can I fix flex duct myself? | You can tape a small, reachable gap with mastic or UL-181 foil tape. Disconnected or crushed runs are better left to a pro. DIY duct sealing guide |
1. Why Ducts Get Damaged
Ducts in attics, crawl spaces and garages take a beating over the years. Flex duct connections loosen as the straps and tape age. People walking or storing boxes in the attic crush and kink runs. Rodents nest in insulation and chew through the inner liner. Heat cycles dry out cloth duct tape until it lets go.
ENERGY STAR estimates that a typical house loses about 20–30% of the air moving through its ducts to leaks, holes and poorly connected ducts. When a run comes fully apart, the room at the end of it can get almost nothing. For more on the causes, see why ducts leak.
2. Types of Duct Damage We Repair
| Problem | What you might notice | How we fix it |
|---|---|---|
| Disconnected duct | One room gets little or no air | Reconnect to the collar or boot, fasten and seal |
| Crushed or kinked flex duct | Weak airflow to one or two rooms | Reroute, support or replace the damaged run |
| Torn liner or jacket | Dust, insulation fibers near registers | Replace the damaged section and re-seal |
| Rodent damage | Droppings, nests, odors | Remove damaged duct and insulation, replace and seal |
| Gaps over 5/8 inch at joints | Air loss Aeroseal can't close | Seal by hand with mastic or UL-181 foil tape |
| Failed cloth duct tape | Loose tape, visible gaps | Remove and re-seal with mastic or foil tape |
ENERGY STAR advises using mastic or UL-181 foil tape, and notes that cloth duct tape is not long-lasting.
3. Flex Duct Repair
Many homes have at least some flexible duct. Flex duct is quick to install, but it's easy to damage. The inner liner tears, the outer jacket cracks in attic heat, and runs that sag or bend sharply lose airflow.
A good flex duct repair does more than tape the tear. We pull back the insulation, reconnect the inner liner to the fitting, fasten it with a strap, seal the joint and pull the insulation and jacket back over it. When a run is badly crushed or chewed, replacing that section is usually the better fix. We also add support where a run sags, because a sagging duct restricts airflow.
If the insulation around your flex duct has failed along a whole run, see our duct insulation page.
4. Why We Combine Hand Repair With Aeroseal
Hand repair and Aeroseal solve different problems. Hand repair fixes damage you can see and reach, including gaps too large for Aeroseal. Aeroseal seals the many small leaks you can't reach, from the inside, while computer monitoring tracks the leakage dropping in real time.
- Hand repair alone leaves hidden leaks inside walls, floors and boots
- Aeroseal alone can't close a disconnected run or a gap over about 5/8 inch
- Both together fix the large damage first, then seal everything else in one visit
Across 38 Bay Area systems MaxSeal sealed, leakage dropped from an average of 400 to 54 CFM25, an 86% reduction (CFM25 = cubic feet per minute of leakage at 25 Pascals of test pressure). Every system gained airflow, by 47% on average. Results vary by home. See the full results study.
5. Step-by-Step: What to Expect
Our Typical Duct Repair and Sealing Process
- Free consultation. We talk about the rooms that bother you and look at your equipment and reachable ducts.
- Baseline test. We measure total leakage with a calibrated Retrotec fan and airflow at every register with a flow hood.
- Hand repair. We reconnect, replace or seal damaged sections and any gap larger than Aeroseal can close.
- Aeroseal sealing. We block the registers, isolate the furnace and coil, and seal the remaining leaks with live computer monitoring.
- Final test. We measure leakage and airflow again.
- Report. You get a before and after report and certificate.
The whole job is usually done in one day per system. Aeroseal recommends occupants not be home during the sealing stage. What to expect on seal day.
6. What a Repair Can Recover
On one system in MaxSeal's data, job H-04, leakage dropped from 485 to 53 CFM25 after sealing. Airflow at the registers went from 238 to 670 CFM, a 182% increase. That's the top of our range. On a system that was already performing well, job M-17, airflow rose by 10%.
Most homes land in between. Systems that start leakier tend to gain more. In our data, systems starting at 450–650 CFM25 gained 64% more airflow on average, and those starting at 250–450 CFM25 gained 36% on average.
7. Repair vs Replacement
Full duct replacement makes sense when most of the ducts are failing, badly undersized or poorly laid out. In many homes the ducts are mostly sound and only a few runs are damaged. Repairing those runs and sealing the rest keeps the existing layout, avoids tearing into walls and ceilings and typically costs much less.
A test tells you which situation you're in. If leakage and airflow numbers show a design problem, a Manual J load calculation and full diagnostic from $495 can show whether the ducts are sized for each room. For a full comparison of the three options, read Aeroseal vs manual duct sealing vs duct replacement.
Conclusion
Damaged ducts rob rooms of air you've already paid to heat or cool. Hand repair fixes the disconnected, crushed, torn and rodent-damaged sections. Aeroseal seals the hidden leaks no one can reach. Together they fix the whole system, usually in one day.
A baseline test shows how much air you're losing and which rooms are paying for it, so you know what the repair will do before we start.
Get a Free Consultation or call (408) 400-3630.
Related: How we repair ducts · Aeroseal vs manual vs replacement · Duct leakage & airflow test · Price list