From the Lab to the Marketplace Ten Years Later, Energy Efficient Technologies from Research at the Lawrence Berkeley National Laboratory Berkeley Lab logo (left) with six rows of gray dots transitioning to a line art drawing of a cityscape and residential houses.

Aerosol Duct Sealing

Leaky ducts allow 15 to 30% of air passing through them to escape, wasting large amounts of energy and increasing both electricity use and emission of pollutants, according to research conducted at Berkeley Lab in the early 1990s. They can also worsen indoor air quality and diminish the ability of heating and cooling systems to maintain comfortable conditions. Before Berkeley Lab scientists calculated the first nationwide estimates of the magnitude of duct leakage in 1986, no one realized that duct leaks were a major source of energy waste. In 1994, Berkeley Lab filed for the first patent for the aerosol sealing technology, a method much superior to sealing ducts manually with existing technologies, such as duct tapes. Since that time, Berkeley Lab researchers have received 3 patents for this technology.

The aerosol duct sealing device attached to a register.

The aerosol duct sealing device is attached to the home's duct system at one of the registers (opening to a room). Other registers are sealed, and the machine blows sealant into the system, sealing leaks at such spots as elbow turns, connecting fittings, and air supply and return chambers. A computer monitors the progress of the sealing.

The aerosol duct sealing machine.

The aerosol duct sealing machine.

Mark Modera, a Berkeley Lab scientist, developed the concept of aerosol duct sealing in 1987, and started funded research in 1990. The process begins with the closing off of the duct system's normal openings (e.g. grilles or registers). Air containing aerosolized adhesive particles in a particular size range is blown into the duct system. This air speeds up and turns sharply when it is forced out of the duct through the leaks. Aerosolized particles, because they are more massive than air molecules, are not able to change direction as easily as air. So, as the particles exit through the leak, they deposit onto its edges. These particles build up and can seal holes as large as one inch across, although the technology is most practical for leaks of less than 3/8 inches across.

Traditional duct sealing methods are time- and labor-intensive. Workers need to go into attics and crawlspaces, find leaks manually, and then seal them one by one. Some duct systems are only partially accessible, or not at all.

Clockwise: poorly installed ducts in an attic, a loosened connecting fitting, and a hole in the duct.

Many types of duct problems—poorly installed ducts, loose fittings, actual breaks in the ducts themselves—can reduce the efficiency of the duct system in a home, resulting in the waste of heating and cooling energy.

Aerosol sealing is more effective and convenient than conventional methods for sealing ducts, because it requires less time and effort, and seals a larger portion of a leakage area more quickly. Workers do not need to inspect the system directly. The process involves sealing up the heating and cooling grilles/registers (the openings between the duct system and the living space of the house), attaching the duct sealing device to a single point, and then measuring the leakage of the system before, during and after blowing sealant into the system. The homeowner or building owner is provided with documentation that the procedure has worked, including the leakage levels before and after sealing, as well as a graph of the sealing process. The entire procedure can be performed within 4 to 8 hours in an existing home.

Sealed systems heat and cool a building more quickly and uniformly, increasing the comfort of the occupants. A sealed duct system may also improve indoor air quality because it reduces the entry of dust, molds, excessive humidity, radon, exhaust gases, pesticides and other chemicals and odors.

In 1997, Berkeley Lab scientist and inventor Mark Modera entered the world of start-up ventures. When the Lab was unable to find an appropriate company to commercialize aerosol duct sealing, Modera took up the challenge and founded Aeroseal Inc.

Infrared photograph of a home shows leaky areas in yellows and reds.

Infrared photograph of a home shows leaky areas in yellows and reds—windows, doors, and roof areas where hot air may be leaking into attic space from leaky ducts.

The development of aerosol duct sealing was only the first hurdle in getting the new technology commercialized. Aeroseal transformed their invention into a marketable product. Aeroseal employees and beta-test contractors tested and sealed ducts all around the country to improve sealing for different types of systems and then developed a computer program to test duct systems for leakage, room airflow problems, combustion safety, air temperature, and return-air performance. This computer program is also used to control, track and document the sealing process. In 1999, Aeroseal began selling the first franchises for the aerosol sealing technology, including training and certifying franchisees to use the computerized duct system diagnostic and sealing technology. Aeroseal was bought by Carrier Corporation in 2001.

Meanwhile, researcher Duo Wang, working with Mark Modera, developed technology that extended the reach of the aerosol sealing technology into the duct systems of larger commercial buildings. These buildings have duct systems that are longer, have a larger cross-section than residential systems, and have many more coils and other equipment that cannot be exposed to aerosol sealant. They developed a sealing system that could perform the atomization inside the ductwork and inject sealant at a much higher rate, thereby extending the applicability of the product to the larger, more complex systems. The resulting product was an induced-cooling pneumatic atomizer that could inject sealant at a smaller spray angle and a higher flow rate. Not finding an appropriate commercially available nozzle, the research team developed their own design, which provided the right particle size and flow rate at the correct spray angle, without clogging.

Rhe aerosol duct sealing system on a commercial building's roof. Workers sealing the duct system of a grocery store. Sealing the duct system in other commercial building sites.

(Top) Testing the aerosol duct sealing system on the roof on a commercial building.

(Center and lower row) Sealing the duct system in a grocery, and in other commercial building sites.

In 2002, Berkeley Lab filed for a patent on the new aerosol sealing technology that was both applicable to large commercial buildings, and could accelerate the sealing process in residences. Carrier-Aeroseal negotiated a license from Berkeley lab to apply this new technology to both residential and commercial buildings the following year. In 2005 Carrier-Aeroseal launched a new version of its original aerosol sealing technology.

When Aeroseal was started, the market did not yet understand the need for Modera's revolutionary technology. Since the market did not yet exist, he set out to stimulate interest in one. He served as chairman of the committee that wrote ASHRAE Standard 152-2004, which standardized calculations of the impact of duct leakage and inadequate duct insulation in residences. With the support of the California Building Industry Association (CBIA), Modera helped produce building code changes for California based upon early versions of ASHRAE Standard 152. Over the course of seven years of meetings and public hearings, Modera and others succeeded in changing California's building code to address energy waste due to leaky ducts. These requirements took effect in 2001 for new construction and in 2005 for existing buildings.

Aeroseal currently seals 3,000 to 4,000 systems per year. Recent projects include sealing ducts in apartment buildings to minimize movement of smells, and in hospitals to decrease the spread of contaminants and biohazards.

More than 25,000 residential duct systems have been sealed to date. With the California building code changes and increasing availability of the aerosol sealing technology, more homeowners and facilities managers will seal their duct systems and save energy each year. Berkeley Lab researchers estimate that by 2020 more than half of the new homes built in the U.S. will incorporate an improved duct design that minimizes leakage. Ducts sealed over the years 2000 to 2020 will save billions of dollars in energy bills annually.

(l) Aeroseal logo; (r) Energy Star logo