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Hot Water Heat - Reverse return piping questions
Looking for help with questions for a hot water heating system with reverse return piping and cast iron radiators.
1) Can the pipe size of the branches and the main supply/return pipes be the same size? e.g. 3/4" mains with 3/4" branches leading to each radiator. Or is it recommended for the branches be a smaller size?
2) Do the total length of the supply main and return main need to be approximately the same length? e.g. can I have 75' of supply piping and only 50' of return piping without causing an issue and having the system remaining as self balancing?
3) Do you typically install a shutoff valve at each radiator? Is it installed on the supply inlet side?
4) Whats the typical copper pipe size used at the inlet and outlet of new 10-20 section 4 column cast iron radiators?
Some background for context....
I'm installing a completely new hot water system for a 3 fam house (2 story, w/ 1000 sqft per floor). Each unit will have its own boiler and reverse return piping. 1st FL is one unit and will have 8 Pensotti wall panel radiators installed. Piping will be copper with 3/4" mains with 1/2' inch branches. 2nd FL will have 2 units (500 sqft per unit), each with its own boiler and pipping and standard cast iron radiators will be installed. My plumber isn't familiar with reverse return piping. He's experienced piping serial systems, mostly for baseboards and cast iron radiators but is willing to try piping reverse return. He wants to use 3/4" pipe for the branches and mains on the 2nd fl. Most examples I found have a smaller branch size vs the main -- will this be a issue? I would like to confirm pipe sizes and lengths seem generally ok.
Are there any other design issues I should consider or bring up with the plumber for a reverse return system? Like... is determining and setting the flow rate gpm the same in a serial system as in a reverse return? Water temp will likely be set at the standard 180 degrees for every boiler. Assume boiler and radiators BTU are properly sized.