Method for manufacturing a conduit element with concentric pipes, in particular for a combustion heating apparatus, the said element being of the type constituted by an inner pipe and by an outer pipe which are mounted coaxially and held with respect to one another by spacer-forming means constituted by a set of pins, the said method comprising: a step of fixing the said spacer-forming means by welding to the periphery of a blank of the said inner pipe; a step of installing the said blank of the said inner pipe on which the said spacer-forming means are fixed into the said outer pipe; and a step of expanding the said inner pipe that consists in an expansion of the said blank of the said inner pipe by means of a tube expansion device, the said expansion bringing each free end of the spacer-forming means into a housing on the inner wall of the said outer pipe, characterized in that it also includes, prior to the installation step, a step of forming an annular groove on the inner wall of the said outer pipe with the aim of creating the said housing in which the free end of the said spacers will be housed during the said expansion step, the said pins constituting the said spacer-forming means being of a length such that, once the said pins have been welded to the periphery of the inner pipe, their free ends are located, before the said expansion step, on a circle with a smaller diameter than the inside diameter of the said outer pipe, and in that it further includes: a step of forming a projecting means in the lower part of the said outer pipe and a step of forming a flared edge at the upper end of the said outer pipe, the said projecting means and the said flared edge being such that the said projecting means of one conduit element is adapted to bear against the said flared edge of the said outer pipe of an underlying conduit element. a step of fixing the said spacer-forming means by welding to the periphery of a blank of the said inner pipe; a step of installing the said blank of the said inner pipe on which the said spacer-forming means are fixed into the said outer pipe; and a step of expanding the said inner pipe that consists in an expansion of the said blank of the said inner pipe by means of a tube expansion device, the said expansion bringing each free end of the spacer-forming means into a housing on the inner wall of the said outer pipe, characterized in that it also includes, prior to the installation step, a step of forming an annular groove on the inner wall of the said outer pipe with the aim of creating the said housing in which the free end of the said spacers will be housed during the said expansion step, the said pins constituting the said spacer-forming means being of a length such that, once the said pins have been welded to the periphery of the inner pipe, their free ends are located, before the said expansion step, on a circle with a smaller diameter than the inside diameter of the said outer pipe, and in that it further includes: a step of forming a projecting means in the lower part of the said outer pipe and a step of forming a flared edge at the upper end of the said outer pipe, the said projecting means and the said flared edge being such that the said projecting means of one conduit element is adapted to bear against the said flared edge of the said outer pipe of an underlying conduit element. a step of forming a projecting means in the lower part of the said outer pipe and a step of forming a flared edge at the upper end of the said outer pipe, the said projecting means and the said flared edge being such that the said projecting means of one conduit element is adapted to bear against the said flared edge of the said outer pipe of an underlying conduit element.