During the Dl-Spacelab mission, several samples of semiconductor and aluminium alloy have been processed in a single ellipsoid mirror furnace (ELLI) and a gradient furnace (GFQ), respectively. Both furnaces operate under inert gas atmosphere at reduced pressure (100 to 200 mbar). In weightlessness, the heat transfer characteristic changed due to absence of convection. For the ELLI, power consumption in space decreased by 15 to 21 %, while the thermal inertia of the system increased by a factor of 2. In contrast to that, the gradient furnace required higher heater temperatures in space, while the influence on the sample thermal profile was rather low.