Duct Sealing Cost: What Moves the Price and What You Actually Get

Duct sealing typically runs $300 to $800 for mastic or tape work on an average Bay Area home, and $1,500 to $4,000 for Aeroseal (the pressurized aerosol method). What you pay depends on how much duct you have, where it is, and which method your contractor uses. Getting a quote after a duct leakage test is the only way to get a real number.

Why Duct Leakage Costs You Money

Most homes lose 20 to 30 percent of conditioned air through leaky ducts before it reaches the rooms you’re trying to heat or cool. That air usually ends up in your attic, crawlspace, or inside walls. Your system runs longer to compensate, which shows up on your PG&E bill and wears out equipment faster. If you’ve had an energy audit, the auditor probably measured your duct leakage with a duct blaster, a calibrated fan that tests the duct system under pressure and reads how much air escapes. That number drives the repair scope.

The Three Methods (and What They Actually Cost)

Mastic sealant is a thick paste, usually gray or white, that a tech brushes over seams and joints by hand. It sets up firm, bonds well to metal and flex duct, and lasts decades when applied properly. It’s the workhorse method for accessible ducts. Bay Area HVAC labor runs $75 to $150 per hour; a focused day of mastic work on attic ducts typically comes in around $500 to $800 depending on access and linear footage. Smaller jobs with easy access can be less.

Foil tape (not the silver stuff from the hardware store, proper UL 181-rated tape) is faster for simple joints, but it can fail at seams that flex or experience temperature swings. Most pros use it in combination with mastic rather than as a standalone fix.

Aeroseal is a pressurized process where a technician temporarily seals all the registers, then injects an aerosolized polymer through the duct system. The particles drift and deposit on any gap they flow through, sealing leaks from the inside. It works well for ducts you can’t physically access, such as those inside walls or under tight floors. The equipment and training cost more, so the price is higher. Bay Area Aeroseal jobs typically start around $1,500 for a smaller home and can reach $3,500 to $4,000 for larger systems or when combined with testing and reporting. Check your local utility’s rebate portal and federal energy efficiency tax credits before paying full price.

What Drives the Price Up

Access is the biggest variable. Attic ducts you can walk around in are cheap to seal. Belly ducts under a crawlspace with six inches of clearance cost more labor time. Ducts buried inside walls or chases almost always require Aeroseal or duct replacement rather than hand-patching.

Duct condition matters too. Old flex duct that’s kinked, compressed, or falling apart isn’t worth sealing, it needs to be replaced. A tech who’s honest will tell you this upfront. Don’t let anyone sell you a sealing job on duct that needs to come out.

System size and linear footage matter, but less than you’d expect. An 1,800 square foot home and a 2,400 square foot home often have similar accessible duct runs in the attic. The square footage number is less useful than the actual duct layout.

What the Tech Should Do Before and After

A professional duct sealing job should include a duct leakage test before and after work. The “before” number establishes the baseline; the “after” number proves the fix worked. California’s Title 24 energy code sets progressively tighter leakage targets for new systems; most older Bay Area homes test at 15 to 35 percent. Getting below 10 percent on a retrofit is realistic and meaningful.

If someone quotes you a price without any mention of testing, ask why. Sealing ducts without measuring leakage is guesswork. You won’t know what you got.

What You Can (and Can’t) Reasonably Do Yourself

You can seal accessible joints at the air handler cabinet, where the main trunk connects to the unit. These are often the worst offenders and are easy to reach. Use mastic (not regular duct tape, which fails) or UL 181-rated foil tape. This won’t address the whole system, but it’s safe to do and genuinely helps.

What you shouldn’t attempt: any duct inside a finished wall, anything in a crawlspace with limited headroom if you’re not comfortable there, and anything involving gas furnace connections or the heat exchanger. Leave Aeroseal entirely to a contractor trained on the equipment. It requires specific training and the polymer needs to be handled correctly.

When to Call a Pro

Call a pro if your energy bills have crept up without an obvious reason, if rooms take significantly longer to heat or cool than they used to, or if you’ve had an energy audit and the duct leakage numbers are over 15 percent. Also worth calling: if your home was built before 1990 and the ducts have never been inspected.

For Bay Area homeowners, duct sealing is one of the higher-ROI home improvements you can make. A properly sealed system can cut HVAC energy use noticeably, and that adds up fast at California electricity rates.

If you want an honest assessment of your duct system, bayareahvacservice.com can send someone to test and quote, no commitment to any particular method until they’ve seen what you actually have.

Key takeaways

• Mastic sealing typically runs $300–$800 for accessible attic ducts; Aeroseal costs $1,500–$4,000 and handles ducts you can't physically reach.
• Access difficulty is the biggest price variable, not home square footage.
• Any reputable job should include a duct leakage test before and after work to prove the fix actually worked.
• Check your local utility's rebate portal and federal energy efficiency tax credits before paying full price for Aeroseal.

Related questions

Written by Andrew Kuznetsov. Andrew is the founder and owner of Bay Area HVAC Service (ADRIUM Service Solutions). He holds a California Contractor License (CSLB #1136642), EPA 608 certification, and completed factory training at the Daikin/Goodman plant in Houston in 2025. He writes from direct field experience, not marketing copy.

Further reading

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