Central heating boiler

A boiler construction comprising, in combination:

• a pair of upright, coaxial wall constructions comprising an outer wall of sheet metal having essentially a cylindrical shape and an inner wall formed for a substantial extent of its length by a group of longitudinally extending stave elements joined by weldments to provide a liquid tight cylindrical upper portion of the inner wall having a predetermined spacing from said outer wall, said inner wall also including a lower portion in the form of a bell shaped skirt of sheet metal defining a combustion chamber welded to said upper portion at the lower end thereof and spaced inwardly from the lower portion of said outer wall, said stave elements defining longitudinally extending flue gas passages at the inner side of said upper portion of the inner wall, which flue gas passages are in communication with the core region of said inner wall portion, and there being a closure means for said core region at that end thereof opposite said combustion chamber;
• and
• wall means joining said inner wall construction to said outer wall construction for forming a water jacket between such inner and outer wall constructions and for relieving the boiler construction of destructive mechanical stresses due to unequal thermal stresses which occur in normal operation of the boiler, said wall means comprising first and second annular wall portions of different radial widths respectively extending radially between the upper end of said upper portion of the inner wall and the outer wall and between the lower end of said combustion chamber and the outer wall whereby the spacing between the inner and outer wall constructions and the spacing between said annular wall portions defines a relatively small volume such that water therein is heated rapidly to temperature, inlet and outlet means for flowing water into said small volume, said skirt which defines the combustion chamber having its upper end of a diameter substantially the same as the diameter of said upper portion of the inner wall and having its lower end of a different diameter so that the radial width of one of the annular wall portions is sufficiently greater than the radial width of the other annular wall portion as to relieve said boiler construction of said destructive thermal and mechanical stresses.