The A. O. Smith's Signature Series, Premium Condensing Gas Tankless line of water heaters, with X3® Scale Prevention Technology, sets a new standard for flexible, efficient, and long-lasting tankless water heating. This product line features our patented X3 ® Scale Prevention Technology, which reduces and eliminates scale buildup due to hard water conditions. This line of water heaters also comes loaded with premium features, such as an integrated recirculation pump, patented heat exchanger, enhanced installation flexibility, and highly efficient performance, making hot water available within an instant at your convenience.