PURPOSE: To provide a method of the manufacture of a flat radiator, wherein a metal foil is adhered on a center of a heat insulating material having a groove for a piping, metal foils are adhered on surfaces of the heat insulating material which is located at opposite sides of the above- mentioned center, after a heat exchange tube has been fitted in the groove, and thereafter a surface material is adhered thereon, so that working efficiency of the manufacture thereof will be improved, and the heat distribution of the obtained radiator will be uniform.

CONSTITUTION: An expandable resin in subjected to expantion molding to obtain a heat insulating material 11 in a flat plate from in which surface a meandered groove 12 is provided for a piping. On a center of the insulating material 11 as well as the inside of the groove 12 is laid an aluminum film 13 both surfaces of which are laminated with polyethylene layers. Then the aluminum film 13 is caused to thermally welded to the insulating material 11. After a synthetic resin tube 14 for hot water has been fitted in the groove 12, aluminum films 15 which has the same constitution as the film 13 are laid along the sides of the mentioned center and on the insulating material 11. After the aluminum films 15 have been thermally welded on the insulating material 11, a surface material 16 of unwoven fabric is laid on all over them. Thereafter, the surface material 16 is thermally welded to the insulating material 11 through the polyethylene layers of the aluminum films 13, 15.