Abstract: An overflow unit for a water heater installation has a plastic, resilient polystyrene pan with a bottom wall for receiving the bottom of the heater and a continuous side wall including inner and outer walls which diverge downwardly in a range of approximately five to fifteen degrees. A bottom edge portion of the outer wall is substantially coplanar with the bottom or outer face of the bottom wall but, preferably, extends outwardly a distance up to approximately 0.0001 inch from the outer face of the bottom wall when the pan is in a relaxed condition. Upon being placed on a supporting surface and receiving the water heater, the bottom edge portion of the outer wall is snugly and closely seated on the supporting surface. A drain coupling for receiving a drain line opens through the inner and outer walls and is in sealed engagement with the inner wall.