In a flat glass laminating oven glass-film sandwiches are located on rotating rollers and conveyed through a heating chamber in a continuous flow. The PVB-film should be heated up to a temperature of 60°C, before it enters to a calender at the end of the oven. Usually heating is arranged with conventional resistors located in a heating chamber. In some ovens the heating is based on forced convection. In them hot air jets are blown toward to glass-film sandwich. Glass and PVB have low thermal conductivity. So, it takes time to transfer heat in to the inner film in a multi-film layer sandwich. The spokespersons of the radiation ovens catch of the problem and express that radiation heating helps, because the radiation penetrates through the glass is absorbed by the film. Clear and low-e coated glass-film sandwiches can be processed with a same speed, is given as an advantage of convection heating. Thus, there exists various kinds of arguments how heating should be arranged. The paper aims to stop the speculations. It shows theoretical results how various glass-film sandwiches heat up in radiation and convection ovens.