One major consideration when installing a floor heating circuit in an existing hydronic system is the need to control water temperature. Most hydronic systems in the U.S. operate at water temperatures necessary for common fin-tube baseboard convectors — usually in the range of 160° to 200°F. In a radiant floor, however, temperatures this high will overheat the slab and possibly cause cracking. Providing lower-temperature water to the floor heating zone, however, may cause flue-gas condensation at the existing boiler. Large-scale floor-heating projects use motor-operated four-way mixing valves and electronic controls costing as much as $1,000. But small projects, such as one-room additions or bathroom remodels, don't have room in the budget for this kind of equipment. Here are two piping strategies for adding
