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Existing Return Sizes a Problem?

swellman Member Posts: 31
edited July 2020 in Radiant Heating
I’ve been working (I think) toward zoning with two circulators. I was reading a bit on primary-secondary piping and am a little concerned having seen this image in connection with a ‘do not’

It’s an existing system so the pipes currently for the return look like this (and I’ve tried to label the pipes based on the Zone they would end up being a part of based on the re-piping I have planned for the supply with the two circulators.

Is it true this looks problematic? My boiler has to take a 1 1/4” return line and I can’t do much about the original line sizes running through much of my house. Should I boycott zoning with circulators at this point?

Blah. So new at this. You guys have been so excellent answering daily to help!


  • GroundUp
    GroundUp Member Posts: 1,924
    The "don't do this" diagram you have there is not primary secondary. With a high head resistance boiler as shown in the diagram, you should not pipe them that way but in a P/S fashion instead. If you have a low head resistance boiler, piping it that way is just fine. There is absolutely nothing wrong with zoning by circ, it just needs to be done properly is all