Fast, Reliable Duct Repair & Sealing Across San Anselmo
Most duct repair calls we take from San Anselmo are not about loud noises or complete failures. They’re about air that smells wrong, rooms that never reach temperature, and energy bills that climb without explanation. If your home was built before 1950 and still runs original or partially updated ductwork through a crawl space, you’re probably living with problems that developed slowly enough to feel normal.
We serve San Anselmo from our Marin County routing, and our technicians are usually on-site within hours, not days. We’ve worked in the Craftsman bungalows along Sir Francis Drake Boulevard, the Victorians tucked between Red Hill Avenue and San Anselmo Avenue, and the hillside homes above the creek corridor in ZIP 94960. We know the difference between a dry hillside crawl space and a damp valley-floor one, and we treat them differently. Call (855) 401-6006 for a free estimate, or read on to understand what your ducts may be costing you.
Why Bellows Air Duct & Vent Co. of California Is San Anselmo’s Preferred Duct Repair & Sealing Company
We’ve been serving Marin County homeowners since 1984, and San Anselmo has been part of our route for decades. Roger Castañeda built this company on a simple standard: show the homeowner exactly what’s wrong before touching a tool, quote one honest price, and stand behind the work for 90 days with no paperwork if something needs adjusting. That standard hasn’t changed.
Our technicians are background-checked, uniformed, and equipped with camera inspection systems that let you see inside your ducts before we begin and after we finish. Most repairs are completed in a single visit. Calls to our office are answered by a live person, 24 hours a day, not a voicemail tree or an app. We’ve earned our reputation in San Anselmo by being the company homeowners call back when they move to a new house, or recommend to a neighbor who got burned by a low-bid operator.
We offer a $50 discount on any repair over $250, a free second opinion on any written estimate, and a permanent 5% senior and veteran discount. Our $89 Seasonal Tune-Up catches small problems before they become expensive ones.
Our Duct Repair & Sealing Services in San Anselmo
Duct Sealing
San Anselmo’s pre-1950s homes were built with sheet-metal ducts joined by mastic that has dried, cracked, or washed out over decades. In the damp crawl spaces near San Anselmo Creek, we’ve found mastic joints so degraded that daylight shows through from the living space above. Our Duct Repair & Sealing team reseals these systems with modern mastic compounds and reinforced tape rated for wet conditions, then pressure-tests to verify the seal. A properly sealed duct system in a 2,000-square-foot San Anselmo home typically reduces HVAC runtime by 15-25%.
Flex Duct Repair
Flex duct is common in additions and retrofits throughout San Anselmo, but it’s vulnerable here in ways that surprise homeowners. The valley-floor humidity between the Marin hills causes the inner insulation layer to delaminate from the plastic core, creating pockets where mold colonies establish and spread. Near the creek, we’ve replaced flex ducts that were compressed by silt deposits left behind after inundation events, cutting airflow to bedrooms by half. We remove damaged sections, install insulated replacement duct with sealed collars, and verify airflow at each register before we leave.
Metal Duct Repair
Original galvanized steel ducts in San Anselmo’s Craftsman and Victorian homes were built to last, but the seams and joints were never designed for the moisture load this valley produces. Rust-through at the bottom of horizontal trunk lines is common where condensation pools. We cut out corroded sections, fabricate replacement pieces on-site, and seal with mastic rather than relying on snap-lock seams alone. Where possible, we slope drain lines to prevent future pooling.
Duct Insulation
Uninsulated or poorly insulated ducts in San Anselmo crawl spaces lose conditioned air before it reaches your rooms. In summer, cool air warms against damp crawl-space surfaces. In winter, heat bleeds into cold, humid air. We install foil-faced fiberglass insulation with sealed vapor barriers, sized for the specific R-value appropriate to Marin’s climate zone. This is especially critical for homes near the creek, where ground moisture keeps crawl-space temperatures lower year-round.
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 Anselmo
We stock parts and materials from Nikro, Honeywell, and Aprilaire on every service vehicle, which means most San Anselmo repairs don’t wait on a parts run. Nikro’s HEPA vacuums and agitation tools handle the heavy debris we find in flood-affected systems. Honeywell and Aprilaire filtration components integrate with existing HVAC setups to capture fine particulate, including the ash and smoke residue that has infiltrated San Anselmo homes during regional fire events. Our technicians carry the right collar sizes, mastic compounds, and insulation wraps for the duct dimensions common in homes built between 1905 and 1950, so we’re not improvising with hardware-store substitutes.
Common Duct Repair & Sealing Problems We See in San Anselmo Homes
- Degraded mastic joints in older sheet-metal ducts allow silt-laden air from flooded crawl spaces to leak into living areas. We find this in homes throughout the 94960 ZIP, especially those with original ductwork from the 1920s-1940s. The mastic hardens, cracks, and falls away, creating gaps that pull in whatever lies beneath the floor.
- Moisture from valley-floor humidity and creek flooding causes flex-duct insulation to delaminate and harbor mold colonies. San Anselmo sits in a natural fog and moisture trap between the Marin hills, and the crawl spaces stay wetter longer than homeowners expect. Flex duct with compromised insulation can’t maintain air temperature and becomes a source of musty odors.
- Pest intrusion is common in pre-1950s duct systems with unsealed joints, made worse by warped floor penetrations that create easy access. Rodents follow the same warm air currents that your furnace pushes, and once inside, they compress insulation, leave debris, and chew through flexible materials. We seal entry points as part of every repair.
- Fine ash and smoke particulate from regional fire events has infiltrated aging duct systems that lack modern filtration. The 2017, 2019, and 2020 fire seasons deposited residue in San Anselmo ductwork that standard filters never caught. Without camera inspection and targeted cleaning, that particulate recirculates every time the system runs.
Pricing for Duct Repair & Sealing in San Anselmo, CA
We believe in one honest price, shown before we start. No bait coupons, no changes at the door.
| Service | Typical Range in San Anselmo |
|---|---|
| Duct sealing (whole system, mastic + tape) | $450 - $850 |
| Flex duct repair / section replacement | $180 - $340 per run |
| Metal duct repair (rust-through, seam failure) | $220 - $480 per section |
| Duct insulation (crawl space, per linear foot) | $8 - $14 |
| Mastic sealant touch-up (localized joints) | $150 - $280 |
| Camera inspection with written report | $89 - $149 |
Costs in San Anselmo run slightly higher than inland Bay Area markets for two reasons: crawl-space access is often tighter in these older homes, and flood or moisture damage frequently requires more extensive material replacement than simple sealing. Homes near San Anselmo Creek with visible silt infiltration typically fall at the upper end of these ranges. We disclose your exact price after inspection and before any work begins. Estimates are free. Call (855) 401-6006 to schedule.
We Also Serve Cities Near San Anselmo
Our technicians cover the full Ross Valley and central Marin County. We regularly repair and seal ductwork in Fairfax, Kentfield, San Rafael, and Larkspur, and we understand how each town’s elevation and exposure change the problems we find. San Anselmo remains our focus on this page, but if you live nearby, the same standards apply. Same live-answer phone, same 90-Day Done Right Promise, same upfront pricing.
Serving San Anselmo, CA - Our Local Coverage Area
We’re based in the San Anselmo 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 Anselmo
If your crawl space took water, your ducts almost certainly did too. Look for musty odors when the system runs, uneven heating or cooling between rooms, or visible rust on floor registers. We recommend a camera inspection to check for silt lines, mold growth, and collapsed flex-duct sections. Call (855) 401-6006 for a free estimate, estimates are free.
Yes. The original mastic in homes built before 1950 was never formulated for the moisture load San Anselmo’s valley-floor climate produces. We use modern, wet-rated mastic compounds and reinforced mesh tape, then pressure-test to verify seal integrity. Call (855) 401-6006 for a free estimate, estimates are free.
Every 10-15 years for homes with original ductwork, or sooner if you notice odors, efficiency drops, or after any flooding event. The persistent moisture in Ross Valley crawl spaces degrades sealant faster than drier inland climates. Call (855) 401-6006 for a free estimate, estimates are free.
Compressed flex duct cannot be restored to original airflow capacity; we replace damaged sections with new insulated duct and sealed collars. We also inspect the full run to identify why debris accumulated, and seal any entry points. Call (855) 401-6006 for a free estimate, estimates are free.
Sealing stops new infiltration but does not remove existing ash residue. We typically combine sealing with HEPA vacuuming and, if needed, sanitizing to address particulate already deposited in the system. For homes affected by the 2017-2020 fire seasons, we’ve found this combined approach significantly reduces recirculation of fine particulate. Call (855) 401-6006 for a free estimate, estimates are free.
We’re ready when you are. Call (855) 401-6006 to speak with a live person, 24 hours a day. We’ll schedule your free estimate, show you exactly what your ducts look like inside, and quote one honest price before any work begins. If it’s not done right, we’ll make it right. That’s the Bellows promise, and we’ve stood behind it for over 42 years.
Written by Roger Castañeda, Owner at Bellows Air Duct & Vent Co. of California, serving San Anselmo since 1984.