Two-sided imaging in laser printers or electrophotographic copiers present design problems at the fusing stage. A typical fuser consists of a pair of counter-rotating rollers forming a nip, a heated roller on the side of the sheet having its image fused, and a pressure roller on the un-imaged or previously-imaged side of the sheet. Through a combination of heat and pressure in the nip, toner particles become viscous. The particles then meld with each other and adhere to the surface of the sheet. As this is happening, it is essential that a previously fused image on the opposite side of the sheet not lose its adherence to the sheet and “offset” to the pressure roller. This article describes the use of an approximate finite-difference numerical model that can be used to predict temperatures in the nip and, consequently, allow the designer to assess the possibility of damage to the opposite-side image. Parameters investigated include toner thickness on both sides of the imaged sheet, sheet thickness and the temperatures of the rollers and sheet.