Electricity energy savings potential by eliminating air leakage from ducts in large commercial buildings is on the order of 10 kWh/m(2) per year (1 kWh/ft(2)). We have tested, in two large commercial buildings, a new technology that simultaneously seals duct leaks and measures effective leak-age area of ducts. The technology is based upon injecting a fog of aerosolized sealant particles into a pressurized duct system. In brief, this process involves blocking all of the intentional openings in a duct system (e.g. diffusers). Therefore, when the system is pressurized, the only place for the air carrying the aerosol particles to exit the system is through the leaks. The key to the technology is to keep the particles suspended within the airstream until they reach the leaks, and then to have them leave the airstream and deposit on the leak sites. The principal finding from this field study was that the aerosol technology is capable of seating the leaks in a large commercial building duct system within a reasonable time frame. In the first building, 66% of the leakage area was sealed within 2.5 h of injection, and in the second building 86% of the leakage area was sealed within 5 h. We also found that the aerosol could be blown through the VAV boxes in the second building without impacting their calibrations or performance, Some remaining questions are: (1) how to achieve sealing rates comparable to those experienced in smaller residential systems; and (2) what tightness level these ducts systems can be brought to by means of aerosol sealing.