Whole-system duct and dryer vent check with before-and-after photos - you see exactly what came out of your vents
That "$99 whole-house special" is a bait ad - the real number appears once they are in your hallway, or the "clean" is a shop-vac at the register. We photograph the inside of your ducts before and after instead.
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AfterFast, Reliable Duct Sealing Across Foster City
Duct sealing in Foster City typically runs $800 – $2,400 for a whole-home seal on slab-on-grade tract homes, and most jobs are completed in a single visit with the price written before we start. We’re the Duct Sealing team at Hollis Air Duct Cleaning, and we serve Foster City from our San Francisco Bay Area dispatch office. Our crews know the engineered fill and bay mud that sit beneath homes in neighborhoods like Marlin, Dolphin Isle, and Edgewater Isle, and we understand why duct sealing here is fundamentally about moisture control, not just stopping air leaks.
Calls are answered by a live person 24 hours a day, 7 days a week. When you’re ready to stop musty odors from cycling through your HVAC, call (361) 326-5060 for a free estimate.
Why Hollis Air Duct Cleaning Is Foster City’s Preferred Duct Sealing Company
We’ve been in business since 2004 as part of the Garrison Partners family, and our track record predates most competitors you’ll find online for Duct Sealing in Foster City. Our technicians are background-checked, uniformed, and expected to arrive inside the quoted window, price the job in writing before touching anything, and leave the site clean. That’s The Garrison Standard, and it’s how every Hollis location operates.
Our 365-Day Done Right Promise covers every duct sealing job in writing. If the seal fails or musty odors return within a year, we come back and make it right at no charge, including a free second visit. No negotiation, no runaround. The price we write down is the price you pay. It does not move at the door.
We use professional-grade equipment from Rotobrush, Nikro, and Abatement Technologies, the same tools commercial crews rely on. For filtration and sealing products, we stock Honeywell, Aprilaire, and Guardsman components. When Foster City homeowners need parts, we don’t order them from a warehouse three states away. Our Bay Area inventory keeps turnaround short.
Duct Repair in Foster City
Duct Repair in Foster City means fixing the original rigid metal ductwork that runs through slab-on-grade homes built between 1960 and 1990, often in tight hallway furnace closets where access is limited and retrofits are common. We see separated seams, corroded boots at the air handler, and gaps where ducts penetrate the slab, all pulling moist air from the engineered fill below. A typical duct repair in Foster City runs $400 – $1,200 depending on accessibility and whether sections need replacement.
Slab-Penetration Seams
These are the failure points we find most often in Foster City. The rigid metal duct meets the concrete slab, and decades of thermal cycling open gaps that suck in ground moisture. We seal with mastic and foil tape rated for damp conditions, then verify with a pressure test or blower motor amp draw. Surface-only tape jobs fail here. We go to the source.
Furnace Closet Retrofits
Original hallway furnace closets in Foster City’s tract homes leave barely enough room to turn around. Our techs carry compact rotary tools and flexible inspection cameras to work in these spaces without tearing out drywall. If a section of duct is too damaged to seal, we cut it out and fabricate a replacement on site.
Air Duct Sealing in Foster City
Air Duct Sealing in Foster City is a moisture-control job first, because the bay mud under this reclaimed marshland keeps crawlspaces and slab perimeters damp year-round while mild summers mean light AC use. That combination lets mold colonize duct interiors during the off-season, so sealing must stop the moisture pathway, not just the air leak. A whole-home air duct sealing in Foster City typically costs $800 – $2,400, with smaller partial seals starting around $450.
Mastic and Mechanical Seal Methods
We brush on duct sealing mastic, a thick, flexible compound that remains pliable and bonds to metal even in humid conditions. For high-stress joints, we reinforce with foil tape. This outlasts hardware-store tape by years. We don’t use aerosol sealants that coat the duct interior and leave homeowners wondering what they just breathed.
Post-Seal Verification
After sealing, we measure static pressure and blower motor amp draw to confirm the system isn’t working harder than it should. In Foster City’s older rigid metal systems, a proper seal often drops amp draw measurably. We show you the numbers before and after. Written down. No guesswork.
Trusted Brands We Service in Foster City
We stock parts and sealing products from Honeywell, Aprilaire, and Guardsman for Foster City homeowners, plus we carry Rotobrush rotary systems and Nikro negative-air equipment for jobs that need cleaning before sealing. Our Bay Area warehouse keeps common fittings and mastic compounds on hand, so we’re not delaying your job waiting for a shipment. When a Foster City home needs a specific boot size or transition fitting for 1960s-era rigid metal duct, we usually have it or can fabricate it same-day. Fast turnaround matters when your house smells like bay mud every time the AC cycles.
Common Duct Sealing Problems We See in Foster City Homes
- Slab-penetration gaps pulling ground moisture. The engineered fill under Foster City’s slab homes stays damp from the bay mud below. Gaps where rigid metal ducts enter the slab act like straws, drawing that moisture directly into the supply air. Sealing only the furnace closet and ignoring these penetrations leaves the problem untouched.
- Failing seams in 35 – 60-year-old original ductwork. Rigid metal ducts in Foster City’s tract homes were built with snap-lock seams and minimal sealing. Decades of thermal expansion and the corrosive salt air from San Francisco Bay have opened longitudinal seams that leak conditioned air and ingest crawlspace humidity.
- “Dirty sock syndrome” after the first warm spring day. We see this every April in Foster City. Homeowners near Marlin Park or along Beach Park Boulevard fire up the AC after a wet winter, and the house fills with musty odor. The cause is microbial growth inside damp ducts, fed by months of moisture infiltration through unsealed gaps.
- Upsold fogging “sanitizers” that mask without fixing. Some outfits spray a chemical fog into the ducts and call it clean. It smells better for two weeks. Then the moisture keeps coming, the mold keeps growing, and the odor returns. We don’t sell fogging as a substitute for sealing the actual leak.
Pricing for Duct Sealing in Foster City, CA
A typical whole-home duct sealing in Foster City runs $800 – $2,400. Partial seals targeting specific problem zones, like slab penetrations or a damaged return trunk, start around $450. What moves the price: how much of the system is accessible without cutting drywall, whether we need to clean before sealing, and if any sections of rigid metal duct are too corroded to seal and must be replaced.
We give one flat price per system, agreed in writing before work starts. No per-vent pricing. No add-ons at the door. The estimate is free, and we explain exactly what we’re sealing and why. Call (361) 326-5060 for an exact quote on your Foster City home.
We Also Serve Cities Near Foster City
Hollis Air Duct Cleaning dispatches crews throughout the Bay Area and beyond. We also provide duct sealing in Los Angeles, San Diego, San Jose, and San Francisco. Scheduling is coordinated from our San Francisco Bay Area office, with local crews serving each metro.
Serving Foster City, CA - Our Local Coverage Area
We’re based in the Foster City 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 About Duct Sealing in Foster City
Foster City was built on reclaimed marshland, and the bay mud under the slab stays damp year-round while the marine layer keeps humidity high. When homeowners turn on the AC after a wet winter, that first airflow pulls mold spores and moisture from duct gaps into every room. Other Peninsula cities with basements or different soil don’t have this chronic ground moisture problem. Call (361) 326-5060 if you’re smelling it this spring, we’ll find the source.
Duct sealing helps with mold and humidity in Foster City because it stops the moisture pathway; a fogging sanitizer only masks odor temporarily. Without sealing the slab penetrations and failed seams, ground moisture keeps entering the system and mold keeps growing. We don’t sell fogging as a standalone fix because we’ve seen it fail repeatedly in Foster City’s slab-on-grade homes. The real solution is sealing first, then verifying the moisture source is cut off.
We use compact inspection cameras and flexible rotary tools designed for tight access, and we fabricate custom fittings on site when original components won’t come apart cleanly. Most Foster City furnace closets are in hallways with less than three feet of working clearance, so our techs are trained to work in confined spaces without damaging surrounding drywall. If a full seal requires access we can’t reach from the closet, we’ll show you exactly why and give you a written option before cutting anything.
You’ll get a written price before any work starts, a camera inspection of accessible ducts, sealing of all reachable joints and penetrations with mastic and foil tape, and post-seal pressure or amp-draw verification to confirm results. The tech will explain what was sealed, what was inaccessible, and what you should monitor. Most Foster City jobs take three to five hours. We leave the site clean and the price doesn’t change from what we wrote down.
Yes, duct sealing is often worth it on original rigid metal ducts because the metal itself lasts; it’s the seams and boots that fail. In Foster City, we’ve sealed original 1960s ductwork that then performed reliably for years because the metal shell was sound and only the joints needed attention. If corrosion has eaten through the metal or sections are collapsed, we’ll tell you during the free estimate and give you a replacement option in writing. Call (361) 326-5060 and we’ll show you what you’re working with.
Written by Roy Castellanos, Owner at Hollis Air Duct Cleaning, serving Foster City since 2004 as part of the Garrison Partners family.