Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Change from steel to pex

I have an old gravity hydronic with 2 1/2" and 3" headers it then branches off to 1" and 3/4" to the other 9 cast iron radiators.. There is a new 130,000 boiler with pump. Could I have any big problems changing all this to 3/4" pex and zone it. i want to get rid of the steel pipes. Thanks for any help.


  • Weezbo
    Weezbo Member Posts: 6,232
    Buenos dias Slowpoke

    He may not be rapid in the feet buh he is very rapid in the mind...

    speedy Gonzales relative : ))

    Muy rapido en la Cabezsa .. yah i like you already ...

    Sure you know what it is even a good thing however , if you have a camera and you have the old piping and boiler near by , i am really big on pictures ..here are some things of interest to me ,

    pipe in and around the boiler room even ones that run back and forth with "U'ies" on the ends of them , The radiators all of them , pipes comming out of the ceiling that are open or thru the roof that are open , pipes that go into small spaces near the top of your system old gauges and mechanisms , the old burner whatever type of fuel ,

    if the walls will be opened up pictures of the verticals that run thu walls to the floor above ,

    then if you can find a way to get the pictures posted here you will find all the help you'd ever want here at heatinghelp there are very few guarantees in life buh i bolieve that one is a Fact Jack : )

    it is a bargin for you , trust me .

    are you doing like a historical reconstruction major overhaul sand blasting the radiators and redoing the floors and adding insulation vapor barrier and dialing in floors and everything ?

    if so , you will find that there are quite a few of us that are definitely into many of the refinements of making your job Showcase ...


    *~//: )
  • Weezbo
    Weezbo Member Posts: 6,232
    i hope i have managed to ,

    contain my enthusiasm for the job.. : )

    i am even interested in the old combustion stack , pieces laying around on the floor , bolted to the floor since you were a child whatever ; ))

    i have some pics for a young guy Paul and i dont know how to get them off my phone and on the wall from my laptop . maybe you can help me with that ,

    do you have a heat loss calc done ? are there any rooms that you are changing partitions in or re arranging the width of stairs or entrance ways that sorta thing ? any over hangs of floors ? interior Pantries? are you located in the hills a town a forest ,

    ok my vans fired up where do you live lol..

    ; )))
  • Slowpoke
    Slowpoke Member Posts: 6
    edited November 2013

    I asked a wrong question? I'm sorry.

    Let me ask another way.

    I want to replace my 90 year old pipes with asbestos on them?

    This is a 2 pipe system.. With 6 cast radiators on 1st.fl. And 3 on the 2nd fl.

    Could I use pex tubing to the radiators, and then insulate them? Is this how they are usually replaced?

  • Weezbo
    Weezbo Member Posts: 6,232
    edited November 2013
    you are fine ,

    there is nothing wrong with your question .

    pex in half inch works for most of the radiators ,

    did that help ?

    Watch out for blind nails through the diagonal flooring and flatten them down and steer Past them so there is no possibility of rubbing on a rusty nail...and plastic squeakers are a must have for the endeavour.

    i like the idea of cutting them off completely and puting aluminum hard drawn plates in the bays to offer some heat distribution on the way to and from the radiators as well ,

    because flow is a good thing i go with the use of bend supports vs hard 90's and i prefer the pls ones that wirsbo makes because you can fasten them with a screw to a board face .

    did any of that help ?


    you can do radiant wall with these plates on the runouts "Tails" some instances instead or as well as , floor warming as a means of increasing comfort .


    manifolds are a good way to do this to an area as well.


    temp gauges are really good add ons as are purges and valves off your manifolds for getting field side air issues under control Early. rather than later the purge (Boiler drains piped in to the manifold/s allows you to clean them up a bit especially if they sit there open to atmosphere for any length of time.


    i like by passes even dummy ones at the manifolds to keep the available water temps right there not back at the boiler .

    insulation is a good item for those run outs ...and where pipe is rolling to another floor and back ..


    find a spot or two ahead of time for the manifold stations ..like a closet or back of a wet wall to aid in keeping potable water lines warmer .

    keep pex off drainage .or heat and sound may migrate ...

    theres some ideas ...
This discussion has been closed.