Sealing Process


We carry out a full system inspection, looking for larger leaks and other factors that need to be addressed before we start our operation. We isolate the section of ductwork to be sealed. We block off all sensing equipment, isolate AHUs/VAVs and block grilles etc with closed cell foam plugs, and cap ductwork ends/branches/VAV boxes.

Fire dampers must be open. Ducts to be sealed need to be clean (3-4mm of debris is fine) and must also be dry and free of grease.

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We use one access/injection point to the ductwork section, and if needed will cut an access hole (ideally 300mm), attach a collar and clamp a length (2.8m) of clear plastic tubing to connect the Aeroseal unit. This unit includes a fan to maintain duct pressure, manometers to measure the pressure differential across the fan, and thermostats and heaters to heat the sealant. Relative humidity is also monitored. A special air compressor connects to the Aeroseal unit, supplying additional air pressure to aerosolise the sealant. The length of plastic tubing between the unit and the duct injection point acts as a mixing zone for the "fog" of sealant which then enters the ductwork.

The information required for the operation of the Aeroseal duct sealing process is:

  • duct material/construction
  • operating pressure (Pa)
  • fan capacity (m3/h)
  • A/C capacity (kW)
  • main equipment model

Pre-seal Air Leakage Test

Using our test equipment at the injection point, we pressurise the duct section and run our pre-seal leakage test. This test gives the air leakage in both L/s and an often more relevant “centimetre squared equivalent hole size”- the total leakage area.

This airflow/leakage information is used within the software that, connected to the Aeroseal unit, drives the sealing process. While we are not independent air leakage testers, our data is very accurate for process reasons.

SmartSeal® software gives live data throughout the Aeroseal sealing process, this monitors ductwork pressure and the reduction in ductwork leakage. If we are unable to maintain the necessary duct pressure to achieve a pre-seal leakage result, this indicates that the leakage is too high to be effectively sealed without modification, so we discuss with our client and identify any missed grilles or larger leak sites that require manual sealing or reduce the size of the duct section and continue.

The test will only take a few minutes and we then commence the sealing process.

How The Sealing Process Works

Via the injection point, the Aeroseal equipment maintains duct pressure (up to 570Pa) and sprays in aerosolised sealant to create a “fog” which fills the duct. This fog of sealant keeps moving within the duct until it accelerates at the bottle-necks (leak points) and deposits at the hole. The sealant bonds to the edges of the leak, then to itself until each leak is completely sealed.

Duct pressure and remaining leakage are continually monitored by the system and two or three onsite technicians to avoid over-saturating the duct.

Where leak sites are in sensitive areas (like computer rooms), we cover any equipment and use a HEPA scrubber fans to pick up any escaping sealant (overspray). It often takes less than an hour to seal a section of ducting.

As a rule, as long as we can pressurise the duct to a minimum of 15Pa, we can seal it. The sealed leaks are plugged with a sealant that resembles silicone and stays strong and flexible, which means duct movement doesn’t reopen the leak sites.
Ducts are usually sealed in sections of about 50 metres, depending on the duct construction, configuration, diameters and leakages involved.

Sealing up to 80% + of the leakage is usually considered a success, but results of around 90% leakage sealed are more common, and we can also tune the process to achieve very high sealing rates (95% + leakage sealed).

Post-seal Results

Once the ducts are considered sealed, we halt the process and run a post- seal leakage test. We will then remove the prep work and return the ducts to service.

We supply both the pre and post seal leakage test results to our clients in a comprehensive report. We guarantee the durability of the Aeroseal sealant for 10 years, and testing in the has shown no detectable deterioration on sealed leaks after 40 years of accelerated conditions.


  • Is safe, stable and has been used to seal ducts in residential, commercial and healthcare facilities for over 20 years.
  • Is mould resistant
  • Is non-flammable and fire resilient
  • Is non-toxic and safe for food preparation areas
  • Is low in VOCs (A+ French VOC rating).
  • Remains effective under a huge range of conditions.
AEROSEAL can reduce the leakage of air conduction systems by an average of 90% in a very short time.
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