Criteria dependencies of the Nusselt number on controlling criteria numbers for two types of electrothermoconvection: in the ideal and poor conducting liquid dielectrics, two types of electromechanical convection: in emulsions and suspensions, and for three types of electroisothermal convection: electric wind, electrification at generalized unipolar convection and at diffusion model are presented. Main peculiarities of heat transfer allowing to calculate the heat transfer process as well as to understand the mechanisms and regularities of EHD phenomena are revealed.