How does Aeroseal seal ducts from the inside?
The duct system is sealed at the registers and pressurized, then an aerosolized sealant is introduced into the airstream. Air escaping through leaks carries the sealant particles to the edges of each gap, where they accumulate and bridge it. Because the process follows the escaping air, it reaches leaks in duct runs buried in attics, walls and slabs that cannot be touched by hand. The technology came out of Lawrence Berkeley National Laboratory, where the aerosol sealing patent was filed in 1994, and the process measures duct leakage before and after — so the result is a number, not an impression.
The short version
- Aeroseal was developed at Lawrence Berkeley National Laboratory, a US Department of Energy national lab. The aerosol sealing patent dates to 1994.
- It seals from inside the pressurized duct system, so it reaches leaks in attic, wall and slab runs that no hand-sealing can get to.
- LBNL measured attic and crawlspace duct systems at roughly 15% leakage on each side of the fan — the exact configuration most Northeast Florida homes have.
- In those systems, sealing produced roughly 15–20% heating and cooling energy savings and over 25% peak electricity demand reduction.
- The sealant bridges holes up to about half an inch across and LBNL reports a service life of 10+ years.
- Leakage is measured before and after, so you get a documented result rather than a claim.
Why duct leakage is the bigger problem in a Florida home
In most Northeast Florida homes, more conditioned air is lost through duct leakage than through anything happening inside the ducts. When supply ducts run through a vented attic — the norm in this region — leaked air is simply gone, and the system pulls replacement air from wherever it can find it. Often that is the attic itself.
That last part matters for air quality as much as for cost. A leaking return in an attic is actively drawing attic air, with everything in it, into the system and distributing it through the house.
Where the technology came from
Aerosol duct sealing was not invented by a marketing department. It came out of Lawrence Berkeley National Laboratory, a US Department of Energy national laboratory, where the aerosol sealing patent was filed in 1994. Mark Modera, the inventor, founded Aeroseal in 1997 under an exclusive licence and the process reached HVAC contractors from 1999.
That origin is worth knowing because it means the performance figures come from national-laboratory measurement rather than vendor literature.
What the measurements actually showed
LBNL's residential work separated duct systems by where they run, and the attic and crawlspace numbers are the ones that describe Florida construction. Those systems measured roughly 15% leakage on each side of the fan. Sealing them produced about 15–20% heating and cooling energy savings, and cut peak electricity demand by more than 25%.
Peak demand is the figure most people skip past, and in Florida it is arguably the most interesting one — it is the hottest part of the afternoon, when the system is working hardest and the grid is most strained, that the savings land.
On the commercial side, the same research reported an average of 87% of leaks sealed across a range of system types.
What the sealant is and what it can close
The cured sealant stays rubbery rather than going brittle, bridges holes up to roughly half an inch across, and LBNL reports a service life beyond ten years. It is not a structural repair: a disconnected duct, a crushed flex run or a hole bigger than the process is designed for needs a physical fix first, and we will tell you if that is what your system has.
Cleaning comes first
Sealant should not be applied over a dirty duct interior. If the system needs cleaning, that happens first, in that order. Any company offering to seal a system without looking at its condition is skipping a step that affects whether the seal holds.
How the job runs
Registers are sealed off and the system is isolated. Duct leakage is measured. Accessible joints and plenum connections are hand-sealed with mastic. The system is pressurized and the aerosol introduced. Leakage is measured again. You get both numbers.
What you should expect to be told
If the pre-seal measurement shows your system is already reasonably tight, sealing it is not worth your money, and that is what we will say. The measurement exists to answer the question honestly, not to justify the job.
See us in action
What the national-lab research found
Hand sealing vs Aeroseal
| Hand sealing with mastic | Aeroseal | |
|---|---|---|
| Where it works | Joints and connections a technician can physically reach | Anywhere air is escaping, including buried attic, wall and slab runs |
| How leaks are found | By eye, where access allows | By the escaping air itself — the sealant goes where the leak is |
| Typical access limit | Plenum connections, accessible boots, exposed joints | No access limit inside the duct system |
| Result measurement | Visual confirmation | Duct leakage measured before and after, in numbers |
| Best used for | Large, visible gaps and plenum connections | The many small leaks spread through an inaccessible system |
These are not alternatives. A thorough job uses both: mastic on the big accessible gaps, Aeroseal for everything behind drywall and insulation. Anyone presenting it as either/or is selling one of them.
At a glance
- Method
- Aerosolized sealant applied from inside the pressurized duct system
- Developed at
- Lawrence Berkeley National Laboratory, patent 1994
- Reaches
- Leaks in attic, wall and slab runs that cannot be accessed by hand
- Seals holes
- Up to roughly half an inch across
- Reported sealant life
- 10+ years (LBNL)
- Measurement
- Duct leakage measured before and after
- Prerequisite
- Duct interior cleaned first where condition requires it
- Also available
- Commercial systems
What the service covers
- Pre-seal duct leakage measurement
- Manual sealing of accessible joints and connections
- Aeroseal application through the pressurized system
- Post-seal leakage measurement
- Documented before-and-after results
Common questions
Is Aeroseal better than sealing ducts by hand?
They solve different halves of the same problem. Hand sealing with mastic is right for accessible joints, plenum connections and boots. Aeroseal handles everything you cannot reach — which in a typical Florida home is most of the duct system. A thorough job uses both rather than choosing between them.
How much duct leakage is normal?
LBNL measured attic and crawlspace duct systems at roughly 15% leakage on each side of the fan. Basement systems ran closer to 30%. Northeast Florida homes are overwhelmingly the attic case. Your own number comes from the pre-seal measurement rather than an average.
Will sealing my ducts help with humidity?
It can. A leaking return pulling humid attic air into the system is adding a latent load your equipment then has to remove. Sealing that leak removes the source. Whether it resolves a specific humidity complaint depends on equipment sizing and run time as well, which is what the inspection looks at.
Will it lower my power bill?
LBNL measured roughly 15–20% heating and cooling energy savings in attic and crawlspace duct systems, plus more than 25% peak demand reduction. Your result depends on how leaky your system was to begin with — which is exactly why leakage is measured before the work rather than estimated after it.
How long does the process take?
Most residential systems are completed in a day. Preparation and measurement take a meaningful share of that; the sealing itself is comparatively quick.
Does the sealant end up in the air we breathe?
The process is designed so the sealant accumulates at the leak edges rather than coating the duct interior. Registers are sealed off and the system is isolated during application. We will discuss timing and occupancy with you when the job is scoped, including any considerations for pets.
Can it seal any size hole?
No. It bridges holes up to roughly half an inch across. A disconnected duct, a crushed flex run or a large tear is a physical repair, and it has to be fixed before sealing rather than instead of it.
How long does the seal last?
LBNL reports a service life beyond ten years, with the cured sealant staying rubbery rather than becoming brittle.
Do I need cleaning and sealing, or just one?
Cleaning removes what is in the ducts; sealing stops what is escaping them. They address different problems and the symptoms overlap. If the inspection shows a clean but leaky system, we will recommend sealing alone — and the reverse.
Sources and standards
Where this page relies on published guidance, here is what it relies on.
- Lawrence Berkeley National Laboratory — Aerosol Duct Sealing — The national-laboratory research the aerosol sealing process came out of, with measured leakage and savings figures.
- US DOE — Minimizing Energy Losses in Ducts — Department of Energy guidance on duct sealing and insulation.
Related services
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Air Duct Cleaning
Cleaning precedes sealing when the interior condition calls for it.
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Duct Replacement & Insulation
When sealing is not enough to save the ductwork.
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Air Duct Inspection
Establishes whether leakage or contamination is the real issue.
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Commercial HVAC System Cleaning
Aeroseal for commercial duct systems.
