Frequent Questions about the duct sealing process and operation

What CAN’T we do?

  • We can't seal greasy ducts. Greasy or very dirty ducts must be cleaned prior to being sealed. Ducts can be a bit dirty before we seal them, but they must be dry and free of grease. We can generally seal kitchen exhaust risers without any issues, but we have look at horizontal kitchen exhaust branches a little more carefully and on a case by case basis. We prefer ComDuc for duct cleaning servicesGo to ComDuc here.
  • We can't provide an independent air tightness test report. We need continuous accurate leakage figures to run the sealing process, so we’re confident our numbers are good. Our clients get a report of their “before and after” leakage numbers. But because we provide a duct-fixing service, we’re not independent testers. We refer people to Airlab for independent testing (www.airlab.co.nz).
  • We can't fully quote an existing, in use building without carrying out a site visit. We need to take prep work into account. We can only give rough figures on information supplied remotely/electronically.
  • We can’t seal a really large/leaky building in one go. Larger buildings usually need to be done in sections, which often minimises business interruption anyway. Sections can be sealed after business hours, and ready for tenant usage the next day. In the US they knocked out a 24-storey hotel in about four weekends, but they had a bigger team than us!
  • We can’t efficiently seal leaks bigger than 15mm.
  • We can’t seal water leaks. Aeroseal is designed for the pressures and characteristics of air.

How long will Aeroseal last, and will just one application last for the lifetime of the ducting?

Aeroseal is guaranteed for ten years under NZ conditions and has been stress-tested for 40 years under accelerated conditions without any delamination or deterioration. As seals remain pliable, they will not be crack or be compromised by duct movement.

What happens to the sealant that escapes leaks, and will it harm my electronics?

Generally, the sealant will escape into ceiling/wall cavities, where small deposits aren’t a problem. We cover sensitive equipment/items as part of our prep work for sealing, ventilate and monitor the area, and use HEPA scrubber fans to pull in and filter air from any overspray zones in living/working areas.

What happens if the leaks are too big for Aeroseal to fix?

We inspect ducting before we start sealing to identify and address broken or disconnected ducts, and generally our initial pre-seal leakage test will indicate the presence of large leak holes too. If a large hidden leak is discovered during sealing, we halt the process and a solution is discussed.

How safe is it?

Aeroseal sealant is a stable, non-toxic, non-flammable emulsion of water and vinyl acetate polymer. It is safe for food preparation areas (US NSF Non-Food Compound Category R2 product listing), is low in VOCs (A+ VOC rating in France, passed European and American regulations and does not off-gas after an initial curing time of two to three hours), it is mould resistant, and passes US smoke and flame spread regulations. The main ingredients in the sealant are also found in chewing gum and hairspray, and Aeroseal has been used in the US for over 20 years in homes, businesses, hotels and medical facilities. Some hospitals even carried out their own research on Aeroseal before giving the go ahead for their ducts to be sealed.

Won’t the sealant coat the inside of the duct?

No. The sealant deposits only at leak sites, where there is a pressure differential between the inside and outside of the duct. This does mean that the sealing process can only occur where there is an air space on the outside of the duct leak, so we can’t seal leaks where the duct is under water or pushed hard against earth/concrete.

Can ducts be cleaned after they have been sealed with Aeroseal?

Yes. However very aggressive methods (like use of caustic chemicals or metal brushes) could compromise the sealant, and so we can’t give a longevity guarantee under these conditions.

General overview of the duct sealing process and operation

General Process

For Project Managers, Energy Consultants/Auditors, Commissioning Agents &, Mechanical Engineers

Detailed Process

Download our supporting documents for technical information (pdf format).

Supporting Documents

Answers to common questions, what we can do & who we recommend for complementary services.


The Duct Sealing Process

"We found the LIMS Aeroseal team quick, efficient and really easy to work with, and the duct sealing process works a treat. We would happily recommend them."

Dave Mather, Manager, Beattie Air Conditioning Ltd