Abstract: Each support plate is provided at its top surface with substantially cylindrical raised portions or protuberances, between which there is present in each case an intermediate space. The raised portions are arranged in rows extending parallel to one another. The raised portions of one row are offset with respect to the raised portions of both neighboring rows. Each of the raised portions have extending therethrough a recess oriented transversely with respect to the rows. Each of the recesses is in alignment with the intermediate space formed between two raised portions of the neighboring rows. The entire top surface of the support plate is covered with a metallic heat conducting layer. In the intermediate spaces and the recesses it is possible to lay, with a random course of extent or travel, the heating pipes or conduits.