Ever notice how hydronics “war stories” get passed around whenever a group of hydronic heating installers are put in the same room? Stories about how a certain job became a real problem over a seemingly insignificant detail? Or about how great — or lousy — a particular product performed? Stories like these are shared only within the strict fraternal confidence of hydronics professionals. I love these stories. They’re a great way of learning how not to repeat a mistake someone else made before you. Here’s a hydronics war story of my own. And yes, (fortunately for me), it has a happy ending.

Several years ago I designed a floor heating system for a new addition to a church. The original building was heated by a steel fire-tube boiler connected to a one-pipe steam system. The boiler had a tankless coil water heater and maintained a minimum standby water temperature year round. The new system would use an indirectly-fired storage water heater in place of the tankless coil. The existing tankless coil was replaced with a new (clean) coil that would serve as the heat source for the floor heating system. This allowed water in the steam system to remain isolated from that in the floor heating system. Not surprisingly, the existing boiler was well oversized, and had plenty of extra heating capacity for the addition. A schematic for the system is shown in Figure 1.