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  1. #1
    Join Date
    Mar 2009
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    231

    Default Replace Cast Iron Heating With PEX?

    I'm looking into finishing my basement and i'm thinking it would look a lot better if I didn't have to build a soffit around old heating pipes. I have a hydronic heating system pushing water to cast iron baseboards and radiators. The basement has older cast iron pips about 1-1/2 inches that then adapt into maybe 1 inch copper before leaving the basement. I'm estimating sizes here but I'm looking for a cheaper way or rerouting these head knocking pipes without the expense of switching to all copper. Would pex work for heating or some alternative?
    My advice and opinions come from hands on knowledge...and This Old House Hidden Content

  2. #2
    Join Date
    Aug 2007
    Location
    The Great White North
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    4,045

    Default Re: Replace Cast Iron Heating With PEX?

    I believe that PEX isn't an issue but rather you would need to install the correct diameter ensuring the gpm flow.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  3. #3
    Join Date
    Feb 2010
    Location
    South*East
    Posts
    1,168

    Default Re: Replace Cast Iron Heating With PEX?

    Is it a one or two pipe system? A two pipe system will have two mains looping around the basement and a one pipe will have just the one line with mono-flow tees. A two pipe system will have larger mains then a one pipe but in ether case, I don't think that you will be able to find any PEX pipe in a size large enough to do the job. As canuk said.

    John

  4. #4
    Join Date
    Mar 2009
    Posts
    231

    Default Re: Replace Cast Iron Heating With PEX?

    Good point guys. It is a 2 pipe system 1-1/4 main feeds that split to 3/4 to the rest of the house. Any other options besides expensive copper?
    My advice and opinions come from hands on knowledge...and This Old House Hidden Content

  5. #5
    Join Date
    Mar 2009
    Posts
    231

    Default Re: Replace Cast Iron Heating With PEX?

    I just thought of something. What determines the size that the main trunk has to be? For example, on one size it's a 1-1/4 pipe from the boiler and about 12 feet away it converts down to 3/4 with no other branches on that side so I assume I can cut cost by shrinking that 12 feet to 3/4 along its length. The other side has 1-1/4 that branches into 3 other feeds of 3/4 so I assume this would have to stay 1-1/4 to maintain the gpm.

    I guess my question may be, if I don't truly need all of the copper, how can I calculate how big the pipe should be so i'm not wasting money on pipe that's too big anyway?
    Last edited by dcalabro; 04-10-2012 at 02:42 PM.
    My advice and opinions come from hands on knowledge...and This Old House Hidden Content

  6. #6
    Join Date
    May 2011
    Posts
    251

    Default Re: Replace Cast Iron Heating With PEX?

    TO properly sizing piping you would need to know what flow rates your'e trying to achieve. Then you have to know the pressure rise or "head" of the circulation pump then subtract the pressure drop or equivalent head of the lengths of pipe your installing.

    To do it right, you'll probably want to get a book on it.
    1925 Two-Story Stucco Beaux Arts Neoclassical

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