In many San Leandro homes the ducts run through an attic or crawlspace that nobody visits. Over the years runs come loose at their fittings, flex duct gets stepped on, kinks or sags, old tape dries out, and rodents chew through the insulation. The furnace and air conditioner keep running, but part of the air they produce warms or cools the attic instead of your rooms. Duct repair finds those spots and closes them up.
Signs your ducts need attention
- One or two rooms are always too warm or too cold, while the rest of the house is fine.
- Some registers blow hard and others barely move air.
- The house gets dusty quickly, especially near the return grilles.
- Ducts rattle, bang when the blower starts or stops, or whistle at a grille.
- Energy bills climb without any change in how you use the system.
- The system runs long cycles and the house is slow to reach the setting.
A room that never cools on a warm afternoon or never warms on a cold morning is worth checking at the ducts before anyone suggests a bigger unit. Our pages on AC not cooling and furnace not heating cover the equipment side.
What we find most often
| Problem | What it causes | Usual fix |
|---|---|---|
| Run disconnected at the register boot or plenum | Little or no air in that room | Reconnect on a metal collar, seal with mastic and secure with a strap |
| Crushed or kinked flex duct | Weak airflow at one register | Replace the section and re-route it with proper support |
| Flex duct sagging between supports | Reduced airflow over a long run | Re-hang it straight with wider straps at regular intervals |
| Old cloth tape failing at seams | Leaks at every joint | Clean and seal with mastic or rated foil tape |
| Torn or missing insulation jacket | Heat loss, and sweating ducts in cooling season | Re-wrap or replace the section |
| Rodent damage in a crawlspace | Leaks, droppings in the air stream, odors | Replace damaged runs once the pests are dealt with |
| Undersized or leaky return | Whistling grilles, low airflow, dust | Seal the return or add return capacity |
How we find the problem
- Walk the attic or crawlspace. Every reachable run, fitting and connection gets looked at, along with the supports and the insulation.
- Room-by-room comparison. Supply temperature and airflow at each register show which runs are underperforming.
- Static pressure. Measuring pressure across the system shows restrictions and undersized returns that a visual check can miss.
- Return side. Gaps around the filter rack and the return plenum pull in unfiltered attic or crawlspace air, so we check them every time.
Then we show you what we found and what we recommend, room by room.
Repair, seal or replace
Repair covers most jobs: reconnecting runs, replacing crushed sections, re-hanging sagging flex and adding a return where the system is starved for air. Sealing follows: duct mastic on seams and connections holds up far longer than cloth duct tape. Replacement of the whole duct system is worth discussing when most of the flex is brittle, flattened or torn inside; at that point chasing leaks run by run stops making sense, and it is quoted as its own project.
Some older homes have duct wrap, tape or joint material that may contain asbestos. If we see suspect material, it should be tested before anyone disturbs it.
What affects the price
Duct repair typically costs $200 to $1,500, depending on the extent of the repairs. Reconnecting and sealing a single run in an easy attic sits at the low end. Replacing several runs, re-hanging long sections, adding a return or working in a tight crawlspace moves the price up. You get the price before work starts, and repairs carry a 90-day warranty.
Repair before cleaning
If the ducts also need duct cleaning, repairs come first. Cleaning works by pulling the duct system under vacuum, which only works when the runs are connected and sealed, and a leaky return would pull dust back in right after the cleaning.
Local notes
Many post-war homes in San Leandro, San Lorenzo and Castro Valley have their ducts in the attic, the crawlspace or both. Attic leaks hurt most on the warm late-summer and fall afternoons, when a disconnected supply run pours cooled air into the hottest part of the house. Crawlspace leaks tend to show up as dust and musty smells, and as rooms that lag behind during the heating months from November to March.