Abstract In 2000, the author and his team reported the effect of the energy from the heat and nip pressure supplied to the toner. They found that, in typical roll fusers, the fuse grade changes very little when the width of the nip is enlarged by reducing the hardness of the pressure roll’s elastic layer without increasing the pressing load. This observation yielded a fuse grade contour in coordinates of heat supply and pressure from which the author could derive design concepts and procedures for basic specifications of roll fusers. This prior study, however, had some outstanding issues: especially in regard to fusing phenomena, the supplied heat is assumed to be equal to the thermal energy used for fusing. However, the absorbed or latent heat should be examined, and rheology should be taken into consideration when this heat is to be compared with the work due to the nip pressure. This article reviews and reconsiders the situation presented in the prior study. It provides a solution describing the roles and effects of thermal energy and work due to nip pressure during toner fusing.