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No flow in moved radiators

CJRS Member Posts: 12
In the situaiton of domestic water or heating I do not see how anyone can use PEX piping. Not sure of yoru exact situatoin but my responce here may make a few assumptions.
Fleible PEX pipe is not the same size comparison first of all. A 3/4" copper has larger I.D> than pex due to wall thickness of the plastic and the fitting have opening of 1/2". So they are not the same as far as flow. If you have a gravity system, firt priority is the pipes sizes were designed large to lessen water flow. Second, the pipes are rigid cause pitch is important in a gravity system. I dont know about using PEX for heating but I willsay this. Maintain your I.D. pipe sizes to assure proper flow. There may be other factors but I dont know enough of yoru system that is being modified for these rads installs.


  • Al Corelli
    Al Corelli Member Posts: 454
    No flow in moved radiators

    Lately, I have witnessed, on four seperate occasions, that radiators moved in remodeling do not heat up. This happens only when PEX has been used.

    I was called to correct a problem last week, where someone moved a radiator from one wall of a small bathroom to the adjacent wall, less than six feet. The 3/4" pex was installed without kinks or sharp bends. The only way to get flow to the radiator, was to add a remote 007 to the take offs from the mains (two pipe, reverse return HW, single zone house)

    In the another house house, a radiator was added (ample capacity) to a two pipe system. The pex was tied in near the boiler (circ on return), no flow was gong through the radiator, even though the attachment points are near the boiler, and should be experiencing enough differential pressure to get adequate flow. Again, added another 007 to correct this. Now, the house shuts down (bad thermostat placement) before the room gets warm.

    The next place was another bathroom renovation where the 3/4" takeoffs were done frm the original radiator and run 15 feet to another location on a different wall. Again, not enough flow.

    All rads are recessed Sunrads. The only difference I can see, is that they are piped in 3/4" pex, rather than copper or IP.

    Am I going crazy? I thought PEX has LESS resistance than the other materials.
  • Dave Stroman
    Dave Stroman Member Posts: 763

    Was it a gravity hot water system?

    Dave in Denver
    Dave Stroman
  • Al Corelli
    Al Corelli Member Posts: 454

    Circs on the return. Two pipe hot water. One is reverse return, the rest are direct return.
  • Had that problem once...

    came to find out that the GC had his guys stuff visqueen plastic inside the radiators to keep dirt and mice out. They somehow missed it and when connected to the system, it plugged the outlet tapping of the radiator. Just enough flow to keep us wondering, and trying different piping schemes to make it work. Finally disassemble the whole shebang, only to find the plastic inside the radiator.

    Some peoples kids...

  • Al Corelli
    Al Corelli Member Posts: 454

    The systems are not gravity, but your mention of the smaller diamer inside the brass PEX fittings seems to have hit home.

    Thank You all.
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