To manufacture a vacuum heat insulated tank adapted to effectively use solar hear for conservation of the global environment in a general atmospheric air by using experiences of the inventor on seam-welding machines, experiences in manufacturing and supplying welding machines for seam-sealing welding of stainless steel sheet metals, experiences in supplying seam-welding machines used for manufacturing vacuum heat insulated vessels in a vacuum tank and other experiences.

According to the method, no limitation is imposed on capacity and complicated equipment is not required for manufacture. From the viewpoint of applications, sun-shining time can be used more effectively than in case of the prior arts. In response to this development, solar water heaters will be rapidly developed and the time when general houses are provided with them will come. Only simple works such as laying of rubber hoses on a roof or the like is required as a very simple means for extracting hot water for utilization. This will prompt the utilization of the solar heat.