Heating chamber in vacuum furnace is closed thermal system where heat exchange is predominantly radiant. Conductive heat exchange is defined by well-known formulas. In order to determine the temperature condition of the object during heating (cooling), it is necessary to determine the angular coefficient of radiant exchange on every other objects. The known in the literature methods, including the geometrical once, have a solution for heat exchange only between two objects. The applications for real heat systems is partial and limited. It is presented a geometric model for calculation the angular coefficients of radiant interchange for closed thermal system. Heat exchange is taking place between an unlimited number of objects and a free-standing arrangement between them. The model allows solutions for objects of different geometric form in the presence of intermediate objects, as well as barriers for heat radiant from their own surfaces. The paper has been verified by a solution of thermal problems for vacuum furnaces.