Due to the fact that the viscosity of non-Newtonian fluids depends on two parameters, the shear rate and the fluid temperature, it is necessary to couple the Navier-Stokes equation with the law of Conservation of Energy to get accurate results in the pressure-throughput calculation of single-screw melt-extruders. In this study a non-isothermal pressure-throughput model will be introduced, considering various parts of the law of Conservation of Energy in down and cross channel direction. The non-isothermal pressure-throughput model will be validated by comparing velocity-, viscosity- and temperature-profiles over the channel height as well as the calculated pressure loss with CFD-simulation results.