Hydronic circulating pumps move water through a closed system of pipes in heating applications or water recirculation systems. The pump is mounted in-line near the boiler and recirculates the water through a closed-loop piping system where water does not exit the pipes. In systems that do not deliver drinkable water, the pipes and pump are constructed of cast iron. These pumps are painted red or green to help identify them as hydronic pumps and are primarily used for radiant heating in residential, commercial, and industrial buildings.