According to A.O. Smith, the proprietary X3 Scale Prevention Technology in its new line of residential gas/propane tankless water-heater units eliminates the need for regular scale-related maintenance (as well as the need for costly isolation valves) and extends the life of the units. The new line is available in three sizes, with maximum Btu/h inputs of 160K, 180K, and 199K. Units operate on a 1/2-inch gas line and vent with 2-inch PVC. They include an integrated recirculation pump and are Energy-Star qualified with UEFs up to 0.93. We found the AT‑160X3P for about $2,300. hotwater.com

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