Patent ID: 6957629

Claim:
A water heater flue comprising: a cylindrical flue defining a cylindrical axis, an interior cylindrical surface, a flue inlet, and a flue outlet, the cylindrical flue having a plurality of mild steel clips welded to the interior surface; wherein each clip has a thickness and generally rectangular shape, the clip having a first short side and a second short side of the same length which are joined by two long sides to define the rectangular shape, the long sides extending from the interior surface radially inwardly substantially toward the axis of the cylindrical flue; wherein the first short side has a portion formed by the thickness of the clip along the first short side which is welded to a portion of the interior surface of the cylindrical flue, and wherein the first short side and second short side are angled about 15° with respect to a projection of the cylindrical flue axis onto the interior surface at the portion of the interior surface of the cylindrical flue; and wherein the first short side and second short side define a plane, the plane intersecting the interior surface of the flue, and wherein the first short side makes an angle of approximately 4° with respect to the intersection of the defined plane and the interior surface of the flue, the clip second short side being displaced upwardly toward the flue inlet; wherein the clips are arranged to form a spiral about the interior of the flue.