In 1994, the Energy Performance of Buildings Group at Lawrence Berkeley National Laboratory invented and developed the aerosol duct sealing technology, a method to internally seal leaky HVAC duct systems. Thousands of duct systems in residential and small commercial buildings have been sealed since the technology was commercialized in 1997. Using the same strategy to seal ducts in large commercial buildings is much more difficult and time consuming than in residential buildings because the duct systems are larger in scale and more complex.To seal duct systems in large commercial buildings, we developed the Mobile Aerosol Sealant Injection System (MASIS), which can perform multiple simultaneous aerosol sealing injection processes. The insertable compact aerosol sealant injector, the essential part of MASIS, has a sealing rate five to ten times higher than that of the commercial injectors. To solve a clogging problem found with commercially available nozzles, we invented the induced-cooling atomizer. This clog-resistant nozzle can be used for other applications as well.The presenter will be discussing the development of MASIS and the custom atomizer.