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Partially draining hydronic system to work on plumbing
I have a hot water heating system with threaded black pipe and cast iron radiators. I have done a bit of work on this system in the past to get it working after past freezes, replacing and eliminating sections of pipe and radiators.
I'm trying to open up two pipes that are currently capped in the basement and I want to know how to determine the least amount of water to drain.
There are no valves to isolate these particular pipes and there is a minumum number of valves in the system.
Being in the basement I would think it would just drain all out if I opened these pipes, but I heard otherwise a while back and was told I drained a ton of water beforehand unnecessarily on a previous occasion.
The purpose of my work today is to install valves at the end of these pipes so I can more easily extend them later on to a new radiator without draining. It is warm today so I don't need heat and I have a little bit of time.