The duct system is pressurized by the Aeroseal machine and sealant-laden air is forced out of cracks and leaks throughout the duct system. As the air leaves the duct, sticky particles are deposited on the leak surfaces and eventually seal those leaks.

Officially, the seal is effective for up to 1/4-in. leaks, but in practice will seal leaks up to 5/8 in. wide given enough time, according to company officials. The mist is blown into the duct system using the same access hole first used to diagnose system leakage.

In 1 to 2 hrs, 70% to 90% of hvac system air leaks are sealed, the company claims. Afterwards, the sealing is confirmed with a pressure test. Customers receive a computer analysis and certificate that their system has been properly sealed.

Safety features

“The material isn’t coating the inside of the duct,” Modera explains. “It remains suspended in the airstream until it reaches leak sites.” The fine powder has been UL tested for erosion, flame and smoke spread, and mold growth, he says.

“Research to develop aerosol duct sealing was funded by the U.S. Environmental Protection Agency, the U.S. Department of Energy, California Institute for Energy Efficiency, and the Electric Power Research Institute (EPRI),” company literature notes. “It has been tested by Underwriters Laboratories Inc. (UL) and the Indoor Environment program at Lawrence Berkeley National Laboratory.”

Modera says he invented the application but not the vinyl acetate polymer, a material which has been blown into ducts for 10 to 15 years in smoke mitigation applications.

Aeroseal provides hvac contractors with training and equipment to perform duct system inspections and certified duct leakage sealing, says Robert Hageman, ceo.

In new construction, no one may check the installed performance of supply or return air functions. Yet if one doesn’t have 400 cfm/ton across the coil, the SEER and capacity ratings (for cooling) may not be valid and certain rooms may not get the air they need.

“When contractors service or replace hvac systems,” Hageman continues, “most perform no check for supply or return flow adequacy (room or total), leakage analysis, register temperature or combustion safety,” all of which may adversely affect performance of the new system or component. He estimates that less than 10% of contractors check such matters.

Aeroseal, he says, has developed a diagnostic software program to perform on-site duct system analysis and also check for proper airflow, combustion safety, return air performance, and other matters.

The ducts and equipment are visually inspected and customers are asked about their indoor comfort and any problems they may have noticed before the duct test begins. The process takes about 90 min and ends with a printed, six-page color summary of the diagnostic results that is easy for the customer to understand.

After the homeowner sees what he/she is losing in system performance, an Aeroseal-trained contractor can produce a workorder on the spot to address the need. Testing and sealing ducts in an “average” single-system residence costs about $500 to $600, Hageman says.

A trained technician can perform duct testing on three average-size homes daily, according to the company. Earlier this year, in cooperation with Houston Power & Light, Aeroseal representatives demonstrated their approach on two homes. One was a 40-year-old, 1,200-sq-ft structure, the other a 25-year-old, 1,600-sq-ft house.

“Both had return side leakage. They were getting about a third of the design airflow directly from the attic. Coils on each system were filthy, yet both had been cared for under annual service contracts with local contractors,” Hageman says.