Aeroseal seals duct leaks from inside the duct system. Registers are temporarily blocked, the ducts are pressurized, and an adhesive aerosol is introduced; as air escapes through leaks, the particles collect at the gap edges and build up until the leak closes. It reaches leaks inside finished walls and ceilings.
The access problem
Duct leakage happens at joints and connections — takeoffs, boots, seams, plenum connections. In an unfinished basement those are reachable and mastic is the right answer. But in a two-story home with branches running through interior walls and ceiling cavities, a large share of the connections are behind finished surfaces. Reaching them physically would mean cutting drywall in a dozen places.
That is the gap this process fills. Instead of getting to each leak from outside the duct, it uses the airflow through the leak itself to carry sealant to exactly where it is needed.
How the process works
- Measure first. The system is pressurized and leakage is quantified. This is the baseline — and it is what makes the result verifiable rather than a matter of trust.
- Protect the equipment. The furnace or air handler and the evaporator coil are isolated so no sealant reaches them.
- Block the registers. Every supply and return opening is temporarily sealed so the duct system becomes a closed, pressurized volume.
- Introduce the aerosol. A fan pressurizes the ducts while atomized adhesive is fed in. Air rushing out through each leak carries particles with it; they strike the edges of the gap, stick, and accumulate.
- Watch it close. Each leak narrows from its edges inward until it seals. Software tracks the leakage rate falling in real time.
- Measure again. Before-and-after numbers and a report.
The thing worth understanding is why the sealant does not just coat the inside of the ducts: particles only deposit where air is moving fast through a narrow opening. In the open bore of a duct, air moves slowly and the particles stay suspended. At a gap, the velocity spikes and they impact and stick. The physics does the targeting.
What it is good for, and what it is not
Good for: the many small-to-moderate leaks distributed across a duct system — the seams, takeoffs and boot connections that collectively add up to the bulk of the loss, especially when they are inaccessible.
Not a fix for:
- A duct that has fallen off its takeoff entirely — that is a hole, not a leak, and needs reconnecting first
- Crushed or kinked flex duct, which is a restriction problem rather than a leakage problem
- Ductwork that is simply undersized for the system's airflow
- Missing insulation on ducts in unconditioned space — sealing stops air loss, not heat transfer through duct walls
- A duct system so deteriorated that replacement is the honest recommendation
Any competent assessment covers these first. If someone proposes aerosol sealing without having looked at the physical condition of the accessible ductwork, that is a reason to ask more questions.
What to expect on the day
Most whole-house jobs take a few hours. Registers are covered during the work, so the system is offline for that period. There is a mild odor during the process that clears as the house ventilates. The sealant is water-based. You get a before-and-after leakage measurement, which is the part worth keeping — it is documentation of what changed.
Is it worth doing in your house?
The homes where this earns its cost most clearly are the ones where ducts run through unconditioned space — attics, vented crawlspaces, garages — because air lost there is lost completely. Two-story homes with a persistently uncomfortable upper floor are the other strong case, since restoring airflow to the far end of the system is often what finally evens the house out.
If your ducts are all inside conditioned space in an open basement, the case is weaker: the leaked air still ends up in the house, and hand-sealing the accessible joints with mastic may be all you need. We would rather tell you that than sell you something.
Smith provides Aeroseal duct sealing and assesses duct condition as part of heating and AC maintenance. Start with what duct leakage costs you if you want the background on why this matters at all.
Frequently asked questions
How does Aeroseal duct sealing work?
Registers are temporarily blocked and the duct system is pressurized while an adhesive aerosol is fed in. Air escaping through each leak carries sealant particles with it, and the particles strike and stick to the edges of the gap, building inward until the leak closes. Leakage is measured before and after the process.
Does Aeroseal get inside my furnace or on my coil?
No. The furnace or air handler and the evaporator coil are isolated before the process begins specifically so no sealant reaches them. The sealant also only deposits where air moves fast through a narrow opening, which is why it collects at leak edges rather than coating the open interior of the ductwork.
How long does duct sealing take and can I stay home?
Most whole-house jobs take a few hours, during which the registers are covered and the HVAC system is offline. There is a mild odor while the work is underway that clears as the house ventilates afterward. The house is normally usable the same day, and the sealant used is water-based.
Is aerosol duct sealing better than sealing by hand?
They do different jobs. Hand-sealing with mastic is the right approach for accessible joints in a basement or crawlspace. Aerosol sealing reaches leaks inside finished walls, ceilings and closed joist bays that cannot be touched physically. A thorough job often uses both, and neither fixes disconnected, crushed or undersized ductwork.