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Replacing 3/4" black Iorn with 3/4" pex

cdoug
cdoug Member Posts: 3
in Radiant Heating
I need to move a 3/4" black iron supply pipe (goes to an upstairs radiator) over about 6 inches. I already have a roll of 3/4" Oxy Barrier Pex. I need to splice in around 8 to 10 ft possibly using a 45 but will try to avoid the 45 if possible. With the ID of the Pex being smaller my question is can I use the 3/4" Pex? If I did use the 3/4 Pex. Do I need to do both supply and return lines so they flow the same? I would just go buy the 1" Oxy barrier Pex and be done with it but I cant find anyplace that sells 20' links in my area. My other thought is that if I did do it in black iron pipe i would need to use 4 elbows. Would that be more restrictive than just running the 3/4" Pex? Thanks

Comments

  • Zman
    Zman Member Posts: 7,610
    How is your system piped? If you have a typical series or parallel piping setup, none of this should matter.
    If it is an old single pipe monoflow system, you should pay attention to these nuances.
    Do you have a picture or a drawing of your arrangement?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Gilmorrie
    Gilmorrie Member Posts: 186
    I would just go ahead with the 3/4" PEX. The I.D. is slightly smaller than black steel, but the pipe wall is smoother, giving somewhat lower pressure drop. I've even made such substitutions for my monoflo system with no problems.

    If the supply is 3/4" steel and the return is 3/4" PEX, don't worry about it. The flow will be the same in each. What goes in must come out.
  • cdoug
    cdoug Member Posts: 3
    It is as older system single mono flow. The Pex would be on the supply line. I thought of a little bit better way so I would only have to splice in about 4 or 5 foot of Pex. I am posting two pics so you get the Idea of what I'm doing. Right now its just a rough cut opening. Thanks
  • Gilmorrie
    Gilmorrie Member Posts: 186
    edited January 2016
    Personally, I think you will be fine. But, if you for some reason don't get adequate flow, install a diverter tee on both the supply and return (oriented in opposite directions).

    Are you sure that is 3/4" steel pipe? It seems like service to a single radiator is often 1/2".
  • cdoug
    cdoug Member Posts: 3
    Yes I'm sure its 3/4" I was shocked when I saw it was that big myself. There are only three radiators upstairs and I found the supplies to the other two, they are both 1/2". Go figure just my luck.

    Thanks

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