Sterling M-6410 is a complete single zone heating/cooling, circulating and control unit, with one delivery and one return line, plus a water supply line and a drain line for cooling. The unit is well suited for use with a city water supply, water from portable or central chillers, towers or with well water. The relatively small total amount of water, rapidly circulated by the Sterl-Tronic, provides assurances of a close and uniform temperature relationship between the delivery and return lines of the unit.