This manual assists engineers in using a computer program, the ESPVI 4.0W, that models all elements of an electrostatic precipitator (ESP). Once an ESP is accurately modeled, the model can be used as an analytical tool to diagnose problems and to suggest ways to improve efficiency. In terms of emissions or electrical use, it can predict the results from various fuels and predict the benefit of equipment additions such as gas conditioning. The manual teaches the engineer how to operate the program and discusses the underlying mathematics. A great deal of attention is given to the practical workings of an ESP. Electrical issues are considered, including the detection and control of reverse ionization, electrode design, and various strategies for controlling and optimizing electric energy use. Mechanical matters such as flue gas cooling and conditioning are discussed as are the characteristics of flue gas that result from various fuels, the particles the flue gases contain, and the electrical qualities of the particles.