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Parallel Flow & Counter Flow Piped Together?
Look at replacing a boiler (300k output) on a one pipe system that has a piping arrangement that I'd never come across before: there are two mains that go left and right off the boiler for about 15 to 20 feet; then each one Tee's horizontally again. Going one way out of the Tee, the pipe slopes downward in parallel flow and loops around until it drops to the wet return. Going the other way out of the Tee, it's piped counterflow about 30 feet and originally supplied two rads and had a main vent. Now, two of the rads on one of the counterflow sides and one on the other side have been removed. the main vent has been removed. Originally, both sides had two rads. We intend on reconnecting these rads.
The system has been down for a year and the present owner is not able to know the long history of the system to tell if there were issues before the rads were removed. Heat pumps have been added which were heating the house for past 15 years.
My question is this: wouldn't this piping arrangement be subject to water hammer if we reconnect all the original rads? It seems to me that the condensate returning from the counterflow would be picked up by steam from the boiler at the Tee and slammed down the parallel flow main.
Again, one side of the counterflow is now capped at the run outs and dead and the other one only has the first rad connected near the main Tee so I can't determine if it had issues before.
My plans are to slope the pipes in question downward and vent them with dry returns on each. That would be included in my bid and eliminate the potential issues, but would not satisfy my curiosity.
What's the opinion of the experts? Has anyone come across this setup?
You can choose to do what you want, but you cannot choose the consequences.