A heat exchange cell for a heating boiler, comprising: - a casing comprising a side wall enclosing an internal space, said side wall having an open front end surrounded by an annular edge of the front end of the casing, - an annular closing flange made from a sheet metal having a flange through opening to allow the access to the inside of the casing, said closing flange defining a radially internal flange edge surrounding said through opening, a radially external flange edge arranged around said radially internal edge, an intermediate flange portion connecting the radially external flange edge and the radially internal flange edge to one another, said radially external flange edge being connected to said side wall of the casing along said annular edge of the front end of the casing, - wherein said radially internal edge defines a radially internal surface, a radially external surface arranged around said radially internal surface, a front edge surface connecting said radially internal surface and said radially external surface to one another, said front edge surface defining a lying plane on which said front edge surface lies, said lying plane defining an axial direction orthogonal to the lying plane and passing through the through opening, and a radial direction orthogonal to the axial direction, wherein the heat exchange cell is characterized in that: - said radially internal surface extends parallel to the axial direction in a manner protruding towards the outside of the cell with respect to said intermediate flange portion; - said radially internal surface and the radially external surface are defined by two respective sheet metal portions, folded with one another in a superimposed double layer, and - said flange is entirely formed in one piece from a single piece of sheet metal by plastic deformation. - a casing comprising a side wall enclosing an internal space, said side wall having an open front end surrounded by an annular edge of the front end of the casing, - an annular closing flange made from a sheet metal having a flange through opening to allow the access to the inside of the casing, said closing flange defining a radially internal flange edge surrounding said through opening, a radially external flange edge arranged around said radially internal edge, an intermediate flange portion connecting the radially external flange edge and the radially internal flange edge to one another, said radially external flange edge being connected to said side wall of the casing along said annular edge of the front end of the casing, - wherein said radially internal edge defines a radially internal surface, a radially external surface arranged around said radially internal surface, a front edge surface connecting said radially internal surface and said radially external surface to one another, said front edge surface defining a lying plane on which said front edge surface lies, said lying plane defining an axial direction orthogonal to the lying plane and passing through the through opening, and a radial direction orthogonal to the axial direction, - said radially internal surface extends parallel to the axial direction in a manner protruding towards the outside of the cell with respect to said intermediate flange portion; - said radially internal surface and the radially external surface are defined by two respective sheet metal portions, folded with one another in a superimposed double layer, and - said flange is entirely formed in one piece from a single piece of sheet metal by plastic deformation.