In recent years, the number of environmental permits mandating the use of natural draft aerial coolers to reduce noise has increased. Natural draft aerial cooler technology can potentially eliminate noise and imporve operational energy efficiency. A broad group of applications could benefit from this technology, including natural gas, engine jacket water, auxiliary water, and engine lube oil cooling. With noise regulations and penalties becoming increasingly stringent, natural draft heat transfer technology is becoming more important. No organization, including Heat Transfer Research, Inc. (HTRI), has as yet fully investigated it.