Abstract: A water heater is provided with a specially designed molded bottom pad/foam dam member which is placed in its bottom pan prior to placing bottom annular portions of the water heater tank and its outwardly spaced jacket structure into the bottom pan. The pad/dam member functions to automatically center the tank relative to its jacket structure, and to prevent leakage past the bottom pan of liquid foam insulation injected into the tank/jacket annulus after bottom end portions of the tank and jacket are secured within the bottom pan. The top side of the pad/dam member has three concentric annular grooves formed therein. The outermost first groove receives an annular bottom end portion of the jacket, while a second groove receives an annular bottom end portion of the tank. The provision of the third groove permits the same pad/dam member to be alternatively used with a water heater having a different tank diameter to thereby improve the manufacturing efficiency of a line of differently sized water heaters.