Fast, Reliable Duct Repair & Sealing Across San Lorenzo
Duct repair and sealing in San Lorenzo typically runs $180–$650 depending on whether you’re dealing with a single joint failure or a full crawl-space replacement, and most jobs we handle in the 94580 ZIP are completed same-day. If you’re losing airflow, smelling mustiness from your vents, or watching your energy bills climb in a Bohannon-era home, the culprit is almost certainly ductwork that’s been sitting in damp crawl space conditions since your forced-air system was retrofitted decades ago. We’re our Duct Repair & Sealing team based in San Francisco with regular routes through San Lorenzo, Ashland, and San Leandro — call us at (855) 908-0725 and we’ll get someone out to diagnose it.
Why Northstar Air Duct Cleaning Service San Francisco Is San Lorenzo’s Preferred Duct Repair & Sealing Company
We’ve been driving down 580 and cutting over to San Lorenzo’s Bohannon tracts for fourteen years. Brian Rivera — owner and lead technician — handles your job personally, not some dispatched crew you’ve never met. That matters when you’re crawling into a 24-inch clearance space under a 1948 ranch house on Via Alamitos or Portola Avenue.
Our numbers are public: 1,209 verified reviews averaging 4.9 stars. That’s not a marketing number — it’s a track record built one crawl space at a time. San Lorenzo homeowners specifically mention our willingness to explain what we found down there, with photos, before any work starts.
Response time to San Lorenzo is typically same-day or next-morning. We’re familiar with the local permit requirements through Alameda County for any duct modifications that alter airflow capacity, and we know which Bohannon floor plans have the worst access points before we even arrive.
Our Duct Repair & Sealing Services in San Lorenzo
Duct Sealing
San Lorenzo’s marine climate turns minor duct leaks into major efficiency drains fast. We seal joints and seams with mastic sealant — not tape, which fails in high-humidity crawl spaces — and we pressure-test before and after to document the improvement. In Bohannon homes near the Bay, we regularly find 15–25% air loss through compromised joints that homeowners attribute to “an old furnace.” Sealing typically runs $180–$340 for a standard single-system home in San Lorenzo.
Flex Duct Repair
This is where San Lorenzo’s housing stock causes unique problems. The flex duct installed during 1970s–1990s HVAC retrofits in Bohannon crawl spaces has spent decades absorbing moisture from soil just feet from San Francisco Bay. We recently reached a Bohannon tract home on Via Alamitos where the flex duct in the crawl space had fully pulled apart at a joint, softened by years of Bay moisture. We replaced the failed section with galvanized metal and sealed all remaining joints with mastic, then insulated the trunk to prevent future condensation. The homeowner hadn’t even noticed the 20% air loss until we performed a pressure test. Flex duct repair or replacement in San Lorenzo ranges from $280–$550 per run.
Metal Duct Repair
Original galvanized trunks in San Lorenzo’s 1940s–1950s Bohannon homes are corroding at seams from salt-laden fog that rolls in regularly. We cut out failed sections, fabricate replacements on-site, and seal with mastic rated for wet environments. Metal repair runs $320–$650 depending on accessibility — low-clearance crawl spaces on streets like Hesperian Boulevard or Lewelling Boulevard take longer but we’re equipped for it with Abatement Technologies portable cutting and crimping tools.
Duct Insulation
Insulation isn’t optional in San Lorenzo. Uninsulated or degraded ductwork in a damp crawl space creates condensation that accelerates mold and re-corrodes what we just fixed. We use foil-faced fiberglass or closed-cell foam wraps rated for marine environments, installed after sealing is complete. Duct insulation for a typical San Lorenzo single-story runs $400–$780.
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 Lorenzo
We don’t show up with hardware-store patch kits. Our San Lorenzo jobs run on Rotobrush and Nikro cleaning and access equipment, Abatement Technologies HEPA containment and cutting tools for metal fabrication, and Honeywell and Aprilaire air quality components when we’re replacing registers or adding filtration. We stock common flex duct diameters, mastic, and galvanized fittings locally — no waiting on parts for standard Bohannon home configurations. Guardsman-grade protective treatments are available for sanitizing after mold remediation in heavily compromised crawl spaces.
Common Duct Repair & Sealing Problems We See in San Lorenzo Homes
- Crawl space flex duct joints softened by marine moisture, causing full separation or collapse. The persistent fog belt around San Lorenzo keeps crawl space humidity above 70% for months. Flex duct connections literally pull apart. We find this on almost every Bohannon-era home we inspect that’s never had duct service.
- Galvanized metal trunks corroding at seams due to salt-laden fog. Original 1940s–1950s metalwork wasn’t designed for Bay-adjacent moisture. Pinhole leaks at seams bleed conditioned air into your crawl space for years before you notice.
- Disconnected or crushed duct sections from water-softened supports. After seasonal rains, saturated soil softens wood or wire supports in low-clearance Bohannon crawl spaces. Ductwork sags, crimps, or detaches entirely.
- Multi-era splice failures where original metal meets retrofitted flex. San Lorenzo’s retrofit history means we often find three connection types in one system — metal, early flex, modern flex — each failing at different rates. The splice points are always the weakest link.
Pricing for Duct Repair & Sealing in San Lorenzo, CA
| Service | Typical Range in San Lorenzo | What Affects Cost |
|---|---|---|
| Duct sealing (mastic, full system) | $180–$340 | Number of joints, crawl space accessibility |
| Flex duct repair/replacement (per run) | $280–$550 | Length, diameter, mold remediation needed |
| Metal duct repair (section replacement) | $320–$650 | Fabrication complexity, clearance constraints |
| Duct insulation (full system) | $400–$780 | Linear footage, material type |
| Combined sealing + insulation | $520–$980 | System size, pre-existing damage |
These ranges reflect San Lorenzo’s specific conditions: smaller square footage (1,100–1,400 sq ft typical), but tighter crawl spaces that add labor time. We don’t quote over the phone without seeing your system — every Bohannon home has a different retrofit history. Estimates are free. Call (855) 908-0725.
We Also Serve Cities Near San Lorenzo
Our regular service radius includes Ashland (94541), San Leandro (94577–94579), Cherryland (94541), and Castro Valley (94546, 94552). Each has different housing stock and moisture profiles — San Leandro’s hillside homes present different duct access challenges than San Lorenzo’s flatland crawl spaces. We adjust our approach accordingly.
Serving San Lorenzo, CA — Our Local Coverage Area
We’re based in the San Lorenzo 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 Lorenzo
San Lorenzo’s Bohannon tract homes were built without central HVAC, so all ductwork was retrofitted into crawl spaces just 2–3 miles from San Francisco Bay. Persistent marine moisture and salt-laden fog keep those crawl spaces damp year-round, softening flex duct connections and corroding metal seams far faster than in drier inland cities like Livermore or Dublin. Call (855) 908-0725 for a free inspection — we’ll show you exactly what your crawl space conditions are doing to your ducts.
Sealing stops air loss at intact joints, but it cannot restore flex duct that’s already collapsed or separated from moisture damage. In San Lorenzo, we typically find that sealing solves 60–70% of the problem; the remaining 30–40% requires section replacement with moisture-resistant materials plus insulation to prevent recurrence. We’ll tell you which category your home falls into before any work starts. Call (855) 908-0725 for an honest assessment.
We seal with professional-grade mastic compounds, repair flex duct with Nikro-compatible replacement materials, fabricate metal repairs using Abatement Technologies cutting and crimping equipment, and install Honeywell and Aprilaire registers or filtration upgrades when needed. For post-mold-remediation protection, Guardsman-grade treatments are available. These are the same tools we deploy on commercial jobs — not the limited kits a generalist HVAC technician carries. Call (855) 908-0725 to discuss what’s right for your system.
Yes — it’s arguably more necessary here than in drier East Bay locations. Uninsulated ductwork in a San Lorenzo crawl space creates condensation that re-corrodes sealed joints and supports mold growth. We insulate after sealing to break that cycle. The added cost ($400–$780 for a typical Bohannon home) pays back in system efficiency and prevented re-repairs. Call (855) 908-0725 and we’ll include insulation in your estimate.
Watch for uneven heating or cooling between rooms, musty odors when the system runs, unexplained energy bill increases, or visible dust accumulation around vents. But the only definitive check is a crawl space inspection — and in San Lorenzo’s low-clearance Bohannon crawl spaces, that’s not a DIY project. We’ve found fully separated ducts that homeowners lived with for years, unaware they were heating their crawl space instead of their bedroom. Call (855) 908-0725 for a free pressure test and visual inspection.
Ready to fix the ductwork that’s been bleeding air and money into your San Lorenzo crawl space? Brian Rivera — owner and lead technician — will handle your job personally, start to finish. No dispatched strangers, no upsell pressure. Call (855) 908-0725 for a free estimate. We’re in San Lorenzo regularly and can usually schedule same-day or next-morning service.
Written by Brian Rivera, Owner at Northstar Air Duct Cleaning Service San Francisco, serving San Lorenzo and the East Bay since 2010.