ABSTRACT?Accurate estimates of heat lost by power equipment facilitate proper sizing of cooling and ventilation equipment required by buildings and industrial plants. Information on heat loss is available in papers published in the 1970s and 1980s@ but some of the information provided in these papers is dated and@ in some cases@ includes overly conservative assumptions. The main focus of this paper is to describe an effort to provide updated information on heat losses by various electric power devices. The information was gathered from equipment manufacturers and relevant standards associated with this equipment. Laboratory tests or mathematical simulations were done to determine heat loss for equipment with insufficient information and to verify published data. A calorimeter was constructed for the testing of equipment. The construction and calibration of the calorimeter are described. Test procedures used in acquiring loss data are described. For each equipment item in the scope of theproject@ a description is provided as to where and how the loss data were obtained. A summary of areas for future investigation is discussed.