Manual duct sealing (mastic and foil tape) runs $400–$1,900 for a professional job on accessible ductwork. Aeroseal runs $1,300–$3,000 and reaches leaks in attic runs and inaccessible trunk lines that manual sealing can’t touch. The right method depends on where your leaks are.
Before you approve ductwork
- 1How did you measure the leakage — a duct blaster test, or a visual estimate?
- 2What’s actually being sealed or replaced, and what’s being left alone?
- 3Can you show me before/after airflow numbers, not just “it’ll feel better”?
- 4Is insulation included where ducts run through unconditioned space?
- 5What’s the warranty on the sealing method or materials used?
- 6Will this change my system’s static pressure, and did you check for that?
What duct sealing costs
| Method | Professional cost | DIY possible? |
|---|---|---|
| Manual (mastic + foil tape) — accessible sections | $400–$1,900 | Yes, with the right materials |
| Aeroseal (injected polymer, whole system) | $1,300–$3,000 | No |
| Combination (manual on accessible, Aeroseal for rest) | $1,500–$3,500 | Partial |
The first rule: not all “duct tape” is duct tape
Standard fabric-backed duct tape does not hold on ductwork. Temperature cycling causes the adhesive to fail within months, often leaving a sticky residue and an open seam. This is documented enough that the DOE and ACCA explicitly recommend against using it.
What works:
- Mastic sealant: A paste applied with a brush or gloved hand that cures to a flexible, durable seal. It bridges gaps up to about 1/4 inch and doesn’t crack with temperature cycling. This is the preferred material for sealing joints and seams.
- Metal-backed foil tape (UL 181 rated): A rigid foil tape with an aggressive adhesive rated for HVAC ductwork. Used to cover larger gaps before mastic, or for areas where mastic is impractical (smooth flex duct connections). Do not confuse with the silver-colored fabric tape sold as “duct tape” — the foil tape is stiffer and has a metallic surface.
Manual sealing: when it works
Manual sealing is the right choice when:
- Leaky joints are in accessible areas (open basement, crawlspace with room to move, attic where duct connections are reachable).
- The duct structure is otherwise intact — no collapsed flex, no completely separated connections.
- A duct leakage test before and after can confirm whether sealing achieved the target.
What manual sealing covers: all visible joints and seams, register boot connections, the air handler cabinet seams, and any penetrations where ductwork passes through walls or floors. A thorough professional job takes 4–8 hours and should include a post-sealing leakage test.
What manual sealing cannot reach: leaks deep inside attic duct runs where there’s no safe access, or connections behind finished walls. These are where Aeroseal has an advantage.
Aeroseal: when the premium is worth it
Aeroseal injects aerosolized polymer particles into a pressurized duct system. As air escapes through leaks, the particles accumulate on the edges of each hole until the hole is sealed. The system measures leakage in real time and stops when the target is reached, giving you a before/after report.
It’s worth the higher cost when:
- A leakage test shows significant leakage and the leaky sections are in inaccessible locations.
- Manual sealing of accessible joints didn’t reduce leakage to target.
- The ductwork is in an attic with no safe walking surface or in areas that would require drywall removal to access.
Aeroseal typically seals 85–95% of measured leakage in a single visit. For a home losing 30% of conditioned air through duct leaks, recovering even 20 percentage points translates to meaningful utility savings and noticeably more even temperatures.
DIY duct sealing
Sealing accessible joints yourself is practical for homeowners who can safely access their ductwork. What you need:
- Water-based mastic sealant (available at HVAC supply houses; brush-grade is easiest to apply)
- UL 181-rated metal foil tape
- Work gloves, a flashlight, and comfortable clothes for crawlspace or attic work
The process: apply mastic to all visible seams and joints by hand, bridging any gaps. Smooth it 2–3 inches on each side of the seam. For larger gaps, apply foil tape first, then cover with mastic. The mastic will be tacky when wet and cure to a firm, flexible coating.
DIY sealing won’t reach inaccessible runs and won’t come with a before/after leakage test. For a system that’s tested at high leakage rates, professional sealing with a verified result is worth the cost.
What to ask before hiring a sealing contractor
- “Will you do a duct leakage test before and after?” Good answer: yes, with specific leakage numbers. Bad answer: “we’ll seal what we can see.”
- “Are you using mastic and foil tape, or Aeroseal?” Know which method you’re getting.
- “What leakage percentage do you expect to achieve?” Good answer: a target number, typically under 10%.
For the full contractor-vetting checklist, see The HVAC Quote Checklist.
If sealing won’t address the extent of your duct problems, the next step is ductwork replacement. To understand whether your airflow symptoms point to ducts at all, see how ductwork works.
Related reading
If a duct-blaster test shows leakage severe enough that sealing alone won’t resolve it, see ductwork replacement cost for when full replacement is the more cost-effective call instead.
