A boiler system includes a support construction and a furnace supported to the support construction at a vertically middle section of the furnace, the furnace being enclosed by water tube walls having two side walls and two end walls, a roof and a bottom, the side walls having a total height (H) from the bottom to the roof. Each of the two side walls has a vertical upper portion that extends from the roof to a level of thirty to seventy percent of the height (H), a lower portion that extends from the bottom to a level of thirty to seventy percent of the height (H) and has a vertical upper portion, and an in downward direction outwards bent intermediate portion at a level between the upper portion of the side wall and the vertical upper portion of the lower portion of the side wall. The support construction includes horizontal wall supporting beams that are arranged parallel to the side walls at a level below the roof of the furnace and directly above the vertical upper portions of the lower portions of the two side walls, and the furnace is supported to the support construction by having the intermediate portions of the side walls connected to adjacent horizontal wall supporting beams so as to balance vertical loads of the furnace.

A waterwall panel welding apparatus is provided. The apparatus includes an inlet assembly, a welding assembly, an outlet assembly, and a heating system. The inlet assembly is for receiving a plurality of tubes. The welding assembly is for receiving the tubes from the inlet assembly and for allowing the tubes to be welded together to form a waterwall panel. The outlet assembly is for receiving the waterwall panel from the welding assembly. The heating system heats the tubes and operates via magnetic induction.