Fast, Reliable Duct Repair & Sealing Across San Bruno
Duct repair and sealing in San Bruno typically runs $180-$650 depending on whether you’re patching a flex-duct leak or replacing a degraded metal trunk line, and most of our San Bruno calls are completed same-day. We’re familiar with the post-WWII tract homes that dominate this city, the persistent marine fog that rolls through the San Bruno Gap, and the particular contamination that comes from living under active SFO flight paths. If your ducts are leaking heated air into a crawlspace, pulling in aviation exhaust, or growing mold behind degraded fiberglass lining, we’ll diagnose it with a camera, show you the footage, and quote the repair before any work begins. Call us at (844) 685-6342.
Why Bellows Air Duct & Vent Co. Is San Bruno’s Preferred Duct Repair & Sealing Company
We’ve been serving San Bruno homeowners since 1984, long enough to have worked on the original duct systems in neighborhoods like Rollingwood, Lomita Park, and the Crestmoor area. Our technicians know which 1950s subdivisions have sheet-metal trunks with failing duct-board lining, which crawlspaces stay damp year-round from Gap moisture, and why standard sealing methods sometimes fail here.
San Bruno customers call us back because we answer the phone 24 hours a day with a live person, not an app or voicemail. Our background-checked, uniformed technicians arrive when we say they will, camera-inspect every duct run before touching a tool, and leave a written record of what was found and what was fixed. The price we quote over the phone is the price on the invoice. No bait coupons, no upsells at the door.
Our 90-Day Done Right Promise covers every repair: if something isn’t right, we return at no charge with no paperwork required. That guarantee has been non-negotiable for over 42 years.
Our Duct Repair & Sealing Services in San Bruno
Duct Sealing
Sealing in San Bruno requires more than slapping mastic on a joint and calling it done. The marine humidity that funnels through the San Bruno Gap keeps crawlspace and attic duct surfaces damp for months at a stretch, which means standard water-based mastic can fail prematurely, often within two years. We use professional-grade sealants rated for high-moisture environments, and we verify every seal with a pressure test and camera inspection. Our Duct Repair & Sealing team checks for the greasy, dark-grey hydrocarbon film we often find in homes under SFO departure paths - if that contamination is present, we clean the plenum before sealing so the mastic bonds to metal, not aviation residue.
Flex Duct Repair
Flex duct installed during later furnace upgrades is common in San Bruno’s older homes, and it’s often the first thing to fail. Moisture from the Gap climate condenses on the inner liner, adding weight that causes sagging or kinking in crawlspaces. A kinked flex duct doesn’t just leak - it can collapse entirely, sending all your heated air into the dirt beneath the house. We replace compromised sections with properly supported, insulated flex duct and seal all connections with mastic and mechanical fasteners. We repaired a flex-duct run in a 1950s home on Elm Avenue where the original duct-board lining had delaminated, allowing humid air from the crawlspace to condense inside the supply trunk. We cut out the compromised section, replaced it with insulated flex duct, and sealed all joints with mastic to prevent the re-entry of aviation-exhaust particulates that had been accumulating for decades.
Metal Duct Repair
The original sheet-metal duct runs in San Bruno’s post-WWII homes were built to last, but the fiberglass duct-board lining inside them wasn’t. After 60-70 years, that lining degrades, sheds fibers into your air stream, and creates a porous surface where mold and biofilm colonize - especially given the combination of Gap humidity and SFO particulates. Spot repair isn’t always possible. Sometimes we can reline a section; sometimes the corrosion and contamination are extensive enough that a partial retrofit makes more sense. We’ll show you the camera footage and explain both options with real numbers before you decide.
Duct Insulation
Uninsulated or damaged duct insulation in San Bruno is a double problem. The damp crawlspace air cools the metal surface, causing condensation that drips onto subflooring and promotes mold. Meanwhile, you’re paying to heat air that loses temperature before it reaches your vents. We install foil-faced fiberglass insulation or closed-cell foam wraps rated for marine climates, sealed at all seams to keep moisture out and conditioned air in.
What happens when you call
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A real person answersNo phone trees - you reach a local pro.
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You get an upfront price rangeHonest numbers before anyone is dispatched.
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A background-checked tech heads outLicensed & insured, dispatched right away.
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You approve before work beginsNothing starts until you say go.
Trusted Brands We Service in San Bruno
We carry parts and materials from Rotobrush, Nikro, and Abatement Technologies - the same brands serious HVAC contractors specify for commercial jobs. For San Bruno homeowners, that means we don’t wait on special orders for most repairs. If your duct system needs a custom fabricated fitting for an odd-sized 1950s trunk line, we can often build it on the truck and complete the job in a single visit. No return trips, no living with a hole in your system overnight.
Common Duct Repair & Sealing Problems We See in San Bruno Homes
- Mastic seals failing within two years. The persistent humidity from the San Bruno Gap keeps duct surfaces damp enough that standard sealants lose adhesion. We see this most often in crawlspace joints on the bay-facing slopes where fog lingers longest.
- Original fiberglass duct-board lining shedding fibers. Those 1940s-1960s tract homes weren’t built with air conditioning, so decades of heating-only cycles let debris accumulate while the lining slowly degraded. The result is a duct that moves air through a deteriorating filter made of its own walls.
- Flex ducts sagging or kinking from moisture weight. Upgraded flex runs in damp crawlspaces absorb atmospheric moisture, get heavy, and pull away from supports. The kink blocks airflow; the sag creates a low point where condensation pools.
- Aviation-exhaust particulate buildup in supply plenums. Homes under the SFO flight path, particularly east of El Camino Real, develop a distinctive dark-grey greasy film that resists standard dry-brush cleaning and can interfere with sealant adhesion if not addressed first.
Pricing for Duct Repair & Sealing in San Bruno, CA
Most San Bruno homeowners want to know what they’re looking at before they call. Here’s what we typically see in this market:
- Spot flex-duct repair (single run, accessible crawlspace): $180-$290
- Mastic sealing of accessible joints (up to 10 points): $220-$350
- Metal duct section replacement with custom fitting: $340-$550
- Duct-board lining removal and metal retrofit (per section): $450-$650
- Duct insulation replacement (per run): $160-$280
What moves the number: accessibility of the duct run, extent of contamination requiring pre-cleaning, and whether we’re working around original 1950s hardware that needs custom fabrication. Every estimate is free, presented upfront, and valid for 30 days. We also honor our standing $50 Off Any Repair Over $250, and we offer a permanent 5% Senior and Veteran discount.
We Also Serve Cities Near San Bruno
Our San Bruno crew regularly works in Millbrae, South San Francisco, Pacifica, and Burlingame. The same flight-path and Gap-humidity conditions affect homes in eastern Millbrae and northern Burlingame, while Pacifica’s direct coastal exposure brings its own duct corrosion patterns. Wherever you are on the mid-Peninsula, we bring the same camera inspection, upfront pricing, and 90-Day Done Right Promise.
Serving San Bruno, CA - Our Local Coverage Area
We’re based in the San Bruno area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
FAQs - Duct Repair & Sealing in San Bruno
That film is likely ultrafine hydrocarbon particulates from jet exhaust settling out of the air column under SFO’s active flight paths, not ordinary household dust. It has a distinct greasy texture and resists standard dry-brush extraction. We HEPA-vacuum and wet-wipe plenum interiors before sealing or cleaning so the surface is actually clean, not just brushed around. Call (844) 685-6342 and we’ll show you the difference on camera.
Sealing is worth it only if the duct-board lining is still structurally intact; if it’s delaminating or shedding fibers, sealing over it traps contamination and the seal will fail as the lining continues to degrade. We camera-inspect first. If the lining is sound, we seal with moisture-rated mastic. If it’s failing, we quote a partial metal retrofit so you’re not throwing good money at a liner that’s already dead. Estimates are free.
The San Bruno Gap channels Pacific moisture straight through town, keeping outdoor relative humidity high even on clear days. That humidity migrates into crawlspaces and attic duct runs, keeping metal surfaces damp and accelerating mold growth inside ducts. It also causes standard mastic to fail prematurely. We account for this by using sealants rated for wet environments and by ensuring all repairs include proper drainage and insulation so condensation doesn’t re-form.
We can seal the leak, but if the sag is caused by moisture weight gain in the liner, the flex duct itself needs replacement or additional support. Sealing a kink without addressing the kink is a temporary fix at best. We’ll install proper hangers, replace waterlogged sections, and route the new run to avoid low points where condensation collects. Call (844) 685-6342 for an exact quote.
If the insulation is water-stained, compressed, or moldy - common in San Bruno’s damp crawlspaces - yes, it should be replaced as part of the repair. Wet insulation loses R-value and becomes a mold reservoir. We install new foil-faced or foam insulation as a standard part of any repair where the old wrap is compromised, sealed at all seams to keep Gap moisture out.
Ready to stop losing heated air into your crawlspace and start breathing cleaner air? Call Bellows Air Duct & Vent Co. at (844) 685-6342 for a free estimate on duct repair and sealing in San Bruno. We’ll camera-inspect your system, show you exactly what we find, and quote one honest price before we lift a single tool.
Written by Ray Castillo, Owner at Bellows Air Duct & Vent Co., serving San Bruno since 1984.