A device used to supply a consistent, lower, pre-regulated water temperature to a radiant system. Mixing valves are most often used in conjunction with high temperature boilers, many designed to heat water to temperatures in excess of 160 degrees. In radiant floor applications, mixing valves do not lower the boiler temperature. Instead, they are plumbed so that the water returning to the boiler from the heated floor branches off to the “cold” side of the mixing valve. In this way the “return” water, after losing much of its heat to the living space, is re-heated to the proper temperature by bleeding small amounts of super hot boiler water into the mixing valve.