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Converted gravity system to mod-con

NYplumber Member Posts: 503
Good afternoon fellow HH members,

I have a converted gravity system at a clients home that we will be changing to a mod con system.

The three inch supply lines on the basement ceiling will be removed, some of the old rads were repiped with copper, yet some of the old supply/return risers will be retained.

Other than adding trv's to the radiators along with a deltaP pump, do I need to be aware of any suprises such as old T's or over sized (diameter) piping?

Thanks in advance,



  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    If more than 1 story tall...

    watch for restrictive orifices in the radiator unions on the upper floors. If they are there, they can cause a complete reversal of flow issues once a pump is added.

    When it was gravity, the hot water had a tendency to flow to the upper floors, starving the lower floors of heat. THe orifices changed this dynamic, and if you add a pump, now the upper floors will be starved for heat, and the lower floors will have a tendency to over heat.

    Be sure and throw a wye strainer in there to catch the biggest chunks, and might not be a bad idea to throw a bypass filter at it to clean up the rust from all the years...

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Ironman
    Ironman Member Posts: 6,868
    I Would Also Add...

    That you make sure that your not still connected to an old expansion tank in the attic and that you flush the old piping thoroughly

    You could also consider a low loss header with dirt and air separation built into it and that would also take care of primary/secondary piping.

    Another thing to look at with TRV's is the need to insulate any piping in un-heated areas. That would be a good idea in any case.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • meplumber
    meplumber Member Posts: 678
    Agree with Bob.

    Make sure that you use a low loss header.  Separating the flow rates is critical.

    I did this same type of conversion once and wasn't aware of a large atmospheric tank in the attic.  Ooops

    I had have good luck with mod/cons in this application.  I prefer a Delta P circ, but that is just personal preference.  Post some pics and let us know how you make out.

    Good Luck.
  • NYplumber
    NYplumber Member Posts: 503

    As you all know from the retrofit I posted along with pictures that I am a fan of deltaP pumps, and low loss headers /  buffer tanks. (LINK)

    I will have to take a look at the attic to see if there is an open tank there.

    If the customer bites the bait, pictures will follow the install.
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