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 Belmont
Duct sealing in Belmont typically runs $450 – $1,200 for a whole-house seal on a standard single-family home, with most jobs completed in a single visit after a written estimate. If your HVAC system is working harder than it should, rooms stay uneven, or your energy bills keep climbing, the problem is often leaks in the ductwork, not the unit itself. Call us at (361) 326-5060 for a free estimate, and we’ll show you exactly where your system is losing air before we quote a fixed price.
We’ve worked on homes from the flatlands near Old County Road to the hillside streets off Ralston Avenue and Alameda de las Pulgas. Belmont’s mix of mid-century ranchers and two-story traditional homes means we’ve seen just about every duct configuration the Peninsula has to offer. Our crews are dispatched from the San Francisco Bay Area office, so we’re familiar with the narrow hillside lots, tight attic accesses, and crawlspace-based systems that are common here. When we say we’ll arrive inside the quoted window, we mean it. That’s The Garrison Standard.
Why Hollis Air Duct Cleaning Is Belmont’s Preferred Duct Sealing Company
We’ve been in business since 2004 as part of the Garrison Partners family, and our reputation in Belmont is built on showing up, pricing in writing, and standing behind the work. Our 365-Day Done Right Promise means if a seal fails within a year, we come back and make it right at no charge, including a free second visit. No negotiation, no runaround.
Our technicians are background-checked and uniformed. You know who’s walking into your home before they arrive. And when you call (361) 326-5060, a live person answers the phone, 24 hours a day, 7 days a week. No voicemail loops, no callback queues, no waiting until Monday for a scheduling question.
We don’t compete on the lowest teaser price. We compete on discipline: arrive when we said, price it before we touch it, do it by the book, leave the site clean. For homeowners who’ve been burned by no-shows, price jumps at the door, or crews who vanished after the job, that operational clarity matters more than any slogan.
HVAC Duct Sealing in Belmont
HVAC Duct Sealing in Belmont is usually a repair-and-seal job, not a simple spray-and-go application, because of the city’s distinctive housing stock. Most Belmont homes were built between the 1940s and 1970s with original galvanized steel trunk lines feeding flexible duct branches in attics and crawlspaces. Decades of thermal cycling, marine-layer damp, and wildfire ash have loosened joints and corroded metal. We find disconnected flex branches, separated collar connections, and pinhole leaks that dump conditioned air into attics and crawlspaces while pulling contaminated air back into the living space.
Our process starts with a camera inspection and static pressure test to map every leak. We use Guardsman mastic-and-mesh sealing on galvanized trunk joints and reconnect or replace degraded flex branches. Every job gets a written price before work begins, and the 365-Day Done Right Promise covers all sealing work for a full year.
What We Find in Older Systems
The galvanized steel in Belmont’s mid-century homes wasn’t designed for fifty-plus years of thermal expansion and contraction. Trunk joints work loose. The marine layer keeps crawlspaces damp year-round, accelerating corrosion at the seams. We often open a system and find the trunk is intact but the connections are leaking 20 – 30 percent of conditioned air. Sealing those joints with proper mastic, not tape, is what restores efficiency.
Smoke Residue Complicates Sealing
After wildfire seasons, we find fine ash particles coating the interior of flex ducts. Sealant applied over that residue traps contaminants against the duct wall. NADCA standards call for source removal and HEPA filtration first, then sealing. Skipping that order is a common shortcut, and it’s one we don’t take.
Duct Repair in Belmont
Duct Repair in Belmont often goes hand-in-hand with sealing because the same age and conditions that cause leaks also cause physical damage. We replace crushed return runs, reconnect detached flex branches, and repair sections of galvanized trunk where corrosion has gone past the point of sealing. In some cases, a section of duct is too far gone and needs replacement before the rest of the system can be properly sealed.
Our equipment includes Rotobrush rotary brush systems and Nikro negative-air machines for cleaning before repair, plus professional-grade mastic and mesh from Guardsman for sealing after. Every repair gets a written price before we start, and the 365-Day Done Right Promise applies to all work.
Crushed and Disconnected Runs
We regularly find flex duct that has been crushed under attic insulation or detached from the trunk collar entirely. The homeowner knows something is wrong because one room never heats or cools properly, but the register boot looks fine. We run a camera to find the real break, reconnect or replace the damaged section, and seal the system as a whole.
When Replacement Beats Repair
Galvanized steel with widespread pinhole corrosion or flex duct that has degraded to the point of tearing needs replacement, not sealing. We’ll show you the camera footage and explain exactly where the line is. No pressure to replace what can be sealed. No false hope that sealing will fix what needs rebuilding.
Trusted Brands We Service in Belmont
We carry professional-grade equipment and materials from Rotobrush, Nikro, and Guardsman, the same brands commercial crews use on larger Peninsula jobs. For filtration upgrades after sealing, we stock Honeywell and Aprilaire products sized for Belmont’s typical residential systems. Having the right parts on the van means we don’t waste your time with supply runs. Most sealing jobs in Belmont are completed in a single visit after the initial inspection and estimate.
Common Duct Sealing Problems We See in Belmont Homes
- Galvanized trunk joints loosened by decades of thermal cycling. The original steel trunk lines in 1940s – 1970s Belmont homes expand and contract with every heating and cooling cycle. The joints work loose, and the resulting leak pulls damp crawlspace air straight into supply and return ducts. Sealing the trunk without addressing the flex branches leaves the biggest loss points open.
- Flex duct branches separating at the collar in hot attics. Belmont’s inland-facing hills get hot, dry summers that degrade flexible duct at the collar connection. Homeowners sometimes seal the register boot but miss the detached branch that’s been dumping conditioned air into the attic and pulling wildfire ash into the run.
- Sealant applied over pre-existing mold or ash residue. After wildfire seasons, fine ash coats duct interiors. Duct sealant sprayed over that residue traps contaminants against the wall. NADCA standards require source removal and HEPA filtration first, then sealing. Skipping that order is a shortcut that costs more later.
- Crushed return runs in tight crawlspaces. Belmont’s hillside lots often have cramped crawlspaces where ductwork has been compressed by storage, pests, or simply decades of settling. A crushed return raises static pressure, strains the blower motor, and reduces airflow to the entire system. We repair the physical damage, then seal the restored system.
Pricing for Duct Sealing in Belmont, CA
A typical whole-house duct sealing in Belmont runs $450 – $1,200, depending on system size, accessibility, and whether repair work is needed before sealing. Single-zone systems in smaller ranchers with good attic access tend toward the lower end. Multi-zone systems in larger hillside homes with tight crawlspaces, or jobs requiring significant repair before sealing, run higher.
We do not quote per-vent pricing. We price per system, in writing, before any work starts. The price does not move at the door. Factors that affect your specific cost include: the number of supply and return runs, whether galvanized trunk repair or flex replacement is needed, accessibility of attic and crawlspace, and whether pre-sealing cleaning is required due to mold or smoke residue.
Every estimate is free. Call (361) 326-5060 to schedule an inspection, and we’ll show you exactly what your system needs and what it will cost.
We Also Serve Cities Near Belmont
Our crews regularly work in Belmont and the surrounding Peninsula communities, including San Carlos, San Mateo, Redwood City, and Burlingame. If you’re just outside city limits or managing a property in one of these neighboring areas, our Duct Sealing team covers the same mid-century housing stock and hillside conditions you’ll find in Belmont.
Serving Belmont, CA - Our Local Coverage Area
We’re based in the Belmont 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 Belmont
Most 1950s galvanized trunk lines in Belmont can be sealed if the metal itself is structurally sound. We see pinhole corrosion at the joints more often than wall failure. A camera inspection shows us where the metal is intact and where it’s too far gone. If replacement is needed, we quote that separately, in writing, before any work starts. Call (361) 326-5060 for a free inspection.
The fine ash particles from wildfire smoke pass through standard HVAC filters and coat the interior of flex ducts. Changing the filter doesn’t remove what’s already inside. We use HEPA vacuums and chemical sponges for source removal, then seal the cleaned system to prevent recontamination. The filter protects the equipment; cleaning protects the ductwork.
Uneven temperatures between rooms, rising energy bills, and dust that returns quickly after cleaning point to leaks. Visible mold or heavy debris calls for cleaning first. We run a static pressure test and camera inspection to separate the two. Often it’s both: clean first, then seal. We quote each phase separately so you know exactly what you’re paying for.
Yes. Belmont’s narrow hillside lots and tight accesses are common here, and our equipment is sized for these conditions. We use compact cameras and flexible tools that fit where standard gear won’t. We’ll inspect the access during our free estimate and tell you upfront if any unusual approach is needed. No surprises after we start.
Most sealed Belmont systems run best with MERV 8 – 11 filters, which catch pollen, dust, and the fine particulates common during wildfire season without overloading the blower motor. Higher MERV ratings restrict airflow and can stress older systems. After we seal your ducts, we’ll recommend the right filter for your specific equipment and the local air quality conditions you face.
Written by Roy Castellanos, Owner at Hollis Air Duct Cleaning, serving Belmont and the Peninsula since 2004.