Fast, Reliable Duct Repair & Sealing Across San Francisco
Duct repair and sealing in San Francisco typically costs $280-$650 for most residential jobs, with same-day or next-day service available throughout the city. Our Duct Repair & Sealing team understands the access challenges of San Francisco’s Victorian flats, Edwardian apartment buildings, and converted warehouse lofts - we’ve been driving these hills since 1984. Call (844) 685-6342 for a free estimate with upfront pricing before any work begins.
San Francisco’s housing stock presents repair problems you won’t find in newer suburban markets. The ductwork in a 1905 Nob Hill flat or a converted SoMa warehouse was never part of the original design. It was shoehorned into wall cavities, floor chases, and crawl spaces never engineered for forced air. Our technicians carry the compact tools and flexible materials needed to work in these tight clearances, and we know the parking and access realities of alley-load buildings and street-sweeping schedules across the city.
Why Bellows Air Duct & Vent Co. Is San Francisco’s Preferred Duct Repair & Sealing Company
We’ve built our reputation in San Francisco on showing up when we say and finishing in one visit. Our 90-Day Done Right Promise means if the repair fails, we return at no charge - no paperwork, no arguing. That guarantee has been stamped on every job since Ray Castillo founded Bellows Air Duct & Vent Co. in 1984.
San Francisco customers tell us they chose us after a bad experience with a low-bid operator who changed the price at the door or disappeared when the job went sideways. We don’t work that way. Our pricing is disclosed before a single tool is lifted. The number on the phone is the number on the invoice.
Most San Francisco calls reach a live person, 24 hours a day - not a voicemail tree, not an app. Our background-checked, uniformed technicians carry camera inspection equipment on every truck, so you see the condition of your ducts before we start and the results after we finish. We serve San Francisco and surrounding communities with the same standard we’ve maintained for over 42 years.
Our Duct Repair & Sealing Services in San Francisco
Duct Sealing
Sealing leaky ducts in San Francisco’s retrofitted systems often delivers the biggest efficiency gain for the lowest cost. In Victorian and Edwardian flats from the Tenderloin to Russian Hill, we’ve found that original sheet-metal connections have loosened over decades, and previous repairs used tape that has dried and failed. Our crew applies mastic sealant and mechanical fasteners designed to flex with the building’s settlement, then verifies the seal with a pressure test. A typical duct sealing job in San Francisco runs $280-$450 for a single-family flat or small multi-unit building.
Metal Duct Repair
San Francisco’s marine fog doesn’t just dampen the sidewalks - it drives chronic moisture into poorly insulated metal duct runs, corroding joints and causing air leaks that waste heated air and draw in crawl-space contaminants. We recently repaired a metal duct run in a Nob Hill Edwardian flat where the fog-driven moisture had corroded the joints and caused a major air leak. Using mastic sealant and a section of new flexible duct, we restored airflow and sealed the system to prevent further moisture intrusion. Metal duct repair in San Francisco typically ranges from $350-$620 depending on access difficulty and the extent of corrosion.
Flex Duct Repair
Flexible ductwork installed during 1970s and 1980s HVAC retrofits is now reaching the end of its service life across San Francisco’s apartment stock. In the Mission District and Noe Valley, we regularly find flex duct that has collapsed, been crushed by storage in tight crawl spaces, or been gnawed by rodents drawn to the warmth. Our replacement flex duct is rated for the cool, moist conditions of San Francisco’s climate and is sized precisely to avoid the sharp bends that trap debris in retrofitted installations. Most flex duct repairs run $320-$580.
Duct Insulation
San Francisco’s persistent fog layer keeps duct surfaces cool enough for condensation to form even in summer, when the South Bay is hitting 90°F. Uninsulated or poorly insulated ductwork in crawl spaces and floor chases drips moisture season after season, creating the mold and mildew problems that define our local market. We install closed-cell insulation and vapor barriers specifically selected for marine climates, with camera verification that the entire run is protected. Duct insulation work in San Francisco generally costs $400-$750 for a typical residential system.
Mastic Sealant Application
For joints and seams that tape can’t hold, mastic sealant is the permanent solution we specify on most San Francisco jobs. Unlike foil tape that degrades in moist conditions, mastic remains flexible and airtight through decades of fog cycles and thermal expansion. We brush or trowel it into every connection on new repairs and existing joints that show leakage during our camera inspection. Mastic application is often bundled with sealing work at $280-$450, or priced separately at $180-$320 for targeted repairs.
Air Leak Repair
Air leaks in San Francisco’s retrofitted duct systems don’t just waste money - they pull in contaminants from crawl spaces, wall cavities, and in mixed-use buildings, from shared shafts adjacent to commercial kitchen exhaust. Our leak detection process uses pressure testing and camera inspection to locate every breach, then matches the repair method to the duct material and access constraints of your specific building. Air leak repair typically falls in the $300-$550 range for San Francisco residential properties.
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 Francisco
We stock parts and specify equipment from Rotobrush, Nikro, and Abatement Technologies - the same brands serious HVAC contractors use when they’re installing systems meant to last. For San Francisco’s moisture-challenged environment, that means corrosion-resistant fasteners, marine-grade mastic formulations, and insulation rated for sustained humidity. We don’t wait on special orders from out of state. Our trucks carry the inventory to complete most San Francisco repairs in a single visit, because we know you don’t want us parking in your loading zone twice.
Common Duct Repair & Sealing Problems We See in San Francisco Homes
- Mold and mildew from fog moisture in uninsulated ducts. San Francisco’s cool marine climate means heating runs lightly and air conditioning rarely runs at all, so ducts sit stagnant while the daily fog cycle drives moisture inside. Without regular airflow to dry them out, poorly insulated runs in Nob Hill and Russian Hill flats become breeding grounds for mold. We find this on camera inspections more often than simple dust accumulation - a pattern essentially unique to this city’s climate.
- Corroded sheet-metal connections in old retrofitted ductwork. The original duct installations in Tenderloin and Mission district apartments used materials and methods adequate for drier inland conditions. Decades of fog-driven moisture have rusted joints and loosened mechanical connections, creating air leaks that worsen every heating season. Repair requires working in tight clearances the original builders never anticipated.
- Grease and cooking particulate coating supply ducts in mixed-use buildings. In Chinatown and the dense corridors of the Mission, residential flats above restaurants draw makeup air through shared shafts and courtyards adjacent to commercial kitchen exhaust. We’ve cleaned supply ducts in apartments where the residents have never cooked a meal, yet the grease film is thick enough to restrict airflow and clog filters. This contamination pattern belongs to San Francisco’s hyper-dense mixed-use building stock alone.
- Collapsed or damaged flex duct from tight crawl-space installations. Victorians and Edwardians in ZIP codes like 94127 and 94102 have crawl spaces and floor chases never designed for ductwork. Original flex duct installations were forced through impossibly tight bends, and subsequent storage or rodent activity has crushed or torn the material. Replacement requires compact tools and flexible materials that can navigate the same constrained paths.
Pricing for Duct Repair & Sealing in San Francisco, CA
Honest pricing means you know the number before we start. Here’s what duct repair and sealing costs in San Francisco’s current market:
| Service | Typical Range in San Francisco |
|---|---|
| Duct sealing (mastic, pressure-tested) | $280-$450 |
| Metal duct repair (corroded joints, leaks) | $350-$620 |
| Flex duct repair/replacement | $320-$580 |
| Duct insulation (marine-grade, vapor barrier) | $400-$750 |
| Mastic sealant application (targeted) | $180-$320 |
| Air leak detection and repair | $300-$550 |
What moves a job toward the higher end: access difficulty (crawl spaces, rooftop units, tight wall cavities), extent of moisture damage requiring mold remediation before repair, and multi-unit buildings where coordination with other residents adds complexity. What keeps costs down: catching problems before corrosion spreads, and bundling related services in one visit.
We offer $50 off any repair over $250, a free second opinion on any written estimate you’ve received, and a permanent 5% senior and veteran discount. Estimates are free. Call (844) 685-6342 for an exact quote on your specific building.
We Also Serve Cities Near San Francisco
Our service area extends throughout the peninsula and central Bay Area. We regularly dispatch to the Mission District, Noe Valley, Chinatown, and Daly City with the same response standards we maintain in our core San Francisco territory. Parking and access logistics vary by neighborhood, and our technicians know the practical details of each - street-sweeping schedules, alley-load requirements, building access protocols. We’ll be there when we say.
Serving San Francisco, CA - Our Local Coverage Area
We’re based in the San Francisco 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 Francisco
San Francisco’s marine fog drives moisture into poorly sealed or uninsulated ducts, and the city’s cool temperatures mean heating systems run lightly while air conditioning almost never runs - so ducts sit stagnant without the airflow that would dry them out. This combination of chronic moisture and stagnant air creates conditions where mold thrives, especially in retrofitted ductwork crammed into floor chases and crawl spaces in Victorian and Edwardian flats. We address this with proper sealing, insulation rated for marine climates, and camera verification that the system is protected. Call (844) 685-6342 for a free inspection - estimates are free.
Yes, our technicians carry compact tools and flexible materials specifically for the constrained access in San Francisco’s pre-1915 housing stock. We’ve worked in crawl spaces under Nob Hill Edwardians where a full-sized technician can barely turn around, and we’ve routed flex duct through floor chases never engineered for HVAC. The key is matching the repair method to the space, not forcing standard approaches into non-standard buildings. Most of these repairs are completed in a single visit. Call (844) 685-6342 to discuss access at your specific property.
Proper duct repair improves security by sealing breaches that could allow entry or surveillance, though our work does not involve security systems directly. In San Francisco’s dense urban environment, we often find duct leaks that pull air from shared wall cavities, elevator shafts, or adjacent units - pathways that compromise both air quality and the physical separation between spaces. Our camera inspection documents the condition before and after repair, and our background-checked technicians respect building access protocols. For security-focused buildings, we coordinate with property managers and follow established entry procedures.
We coordinate with property management and follow commercial-residential interface protocols that protect both restaurant operations and residential air quality. In Chinatown and similar dense mixed-use corridors, we frequently find residential supply ducts contaminated with grease and cooking particulate drawn from shared shafts adjacent to commercial kitchen exhaust. Our repair process includes sealing duct breaches that allow cross-contamination, cleaning affected runs with appropriate methods, and installing filtration upgrades where needed. We schedule work to minimize disruption to ground-floor businesses and respect the access constraints of buildings with single shared entries.
Proper insulation with a vapor barrier, combined with airtight sealing of all joints and connections, prevents the warm, moist air from contacting cool duct surfaces where condensation forms. In San Francisco’s climate, we specify closed-cell insulation and marine-grade mastic sealant rated for sustained humidity, not the products adequate for drier inland markets. We also verify that duct runs have adequate slope for drainage where condensation cannot be fully eliminated. The investment in proper insulation and sealing typically pays back through reduced mold risk and improved heating efficiency within two to three fog seasons. Call (844) 685-6342 for an assessment of your specific duct system.
Ready to fix the leaks, seal the moisture out, and get your San Francisco home’s airflow back to where it should be? Call Bellows Air Duct & Vent Co. at (844) 685-6342 for a free estimate with upfront pricing. We’ll show you the camera footage, explain what needs doing, and give you one honest price before we start. That’s been our way for over 42 years.
Written by Ray Castillo, Owner at Bellows Air Duct & Vent Co., serving San Francisco since 1984.