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Piping layout in hydronic systems is often confusing.
When troubleshooting a hydronic system, the piping layout is often confusing. To understand the system, I sometimes sketch the piping to help me visualize the flow of water. On a particularly complicated job, I will use colored highlighters to help me see the circulation in my mind. The following hydronic jobs were ones that did not work as intended.
Direct return
The service call was at an old home with cast iron radiators. The customer said they had plenty of heat on the first floor, some heat on the second floor and no heat to the third-floor radiators.
"Oh, the Goldilocks and the Three Bears syndrome," I said, laughing.
The owner looked at me like I had three eyes.
"Never mind," I whispered.
My first thought was the system pressure was too low. It takes one pound of pressure to raise water 2.3 feet. The highest radiator was 36 feet above the boiler, which meant the system needed 16 psi, plus 3-4 psi as a safety factor.
The pressure on the PTA gauge read 25 psi, plenty of pressure. After sketching the piping, I realized it was a direct return hydronic system. A direct return system looks like a ladder, and the first radiator fed is the first to return, essentially short-circuiting the system. To avoid that, balancing valves are installed in the piping to restrict the flow through the closest radiators to force more flow to the ones further away.
The original installer used globe valves in the return piping to balance the flow. Someone opened the valve fully on the first floor, so most of the heat was going through...