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New condensing boiler to old piping

Tom ShermanTom Sherman Posts: 6Member
Hi folks,

Hoping you can help me with this question. I have been forward a question related to an old forced hot water system, with the boiler recently replaced with a new condensing boiler. My (and their) question: how is the old larger piping affected by the smaller copper pipe feed in the photo? Does it make any difference once the system is charged with water? Small to large...does this create potential air issues? Are there any ramifications or other things I should be looking at/for with this marriage between old and new? So many questions! I realize this is a small snapshot to go by, but any specific or general thoughts would be welcome and greatly appreciated.


  • GBartGBart Posts: 753Member
    you have to heat all of that water and none of it is insulated, hopefully they piped the primary-secondary loop properly
  • Tom ShermanTom Sherman Posts: 6Member
    Thanks GBart, for the response! Good point on the insulation! I don't know enough about the piping to know whether it is a single loop or has secondary loops. If secondary loops, would anything need to be altered with the installation of a condensing boiler, or would the installation be the same as originally? (Sorry, I know I'm asking questions with very limited information to provide, but this is pretty much all I have to go on) Thanks!
  • Solid_Fuel_ManSolid_Fuel_Man Posts: 1,458Member
    Are you sure it wasn't a gravity water system before?
    Master electrician specialising in boiler and burner controls, multiple fuel systems, radiant system controls, building controls, and universal refrigeration tech.
  • Jamie HallJamie Hall Posts: 10,282Member
    From the look of it, I'm going to bet on a converted gravity system. There may be some weird balancing issues... Otherwise, not really any oddities. You may not get as much efficiency gain with the condensing boiler as you might want to.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • psb75psb75 Posts: 84Member
    Good news: mod/con boilers match up beautifully with older high mass radiation systems (cast iron radiators and large volume piping). But....they must be piped, pumped and controlled in appropriate configurations. Along with modulating, you also want the boiler to CONDENSE as much as possible.
    Find an expert.
  • Danny ScullyDanny Scully Posts: 1,153Member
    edited March 1
    If it were gravity, the rule of thumb is half the existing pipe size, then one size down from that. So if it were 3” let’s say, half of that is 1-1/2”, than 1-1/4” is one size down from that.
  • GBartGBart Posts: 753Member
    You'd have to give us pictures of the near boiler piping, a low mass boiler needs help in taking on that much water, either a return bypass or preferably a primary/secondary loop set up. The most important aspect is that they followed the manufacturers piping instructions, but get that piping insulated ASAP, get the good stuff at HD/Lowes that has white paper backing with fiberglass insulation.

    The attached article explains it, has pics and is written by the one and only HeatingHelp Dan Holohan
  • GBartGBart Posts: 753Member
    this pic shows a primary/secondary loop to a Weil McLain low mass condensing boiler, one loop goes through the system, the second goes through the boiler, they connect at the T's and must be no more than 12" apart, in this way it's an injector loop and the boiler can gain temp while still feeding a MASS system with lots of water, otherwise you'd flush the boiler with cold water and never gain any temp, and you might crack some boilers from sudden temp drop shock.

  • EBEBRATT-EdEBEBRATT-Ed Posts: 5,631Member
    To answer your question if they piped it right and control it right the oversized piping will present no major issues
  • mikeg2015mikeg2015 Posts: 761Member
    Other concerns is ideally they install a good dirt separator and air vent. Boiler will still have a strainer typically, but all that old piping will corrode and you get scale that can plug the strainer. OR worse the heat exchanger.

  • Tom ShermanTom Sherman Posts: 6Member
    Thanks all, for the answers and clarification on this! I realize there is far too little information from this one photo, but I gained a lot of good information. Appreciate it much folks!
  • SuperTechSuperTech Posts: 938Member
    > @Tom Sherman said:
    > Thanks all, for the answers and clarification on this! I realize there is far too little information from this one photo, but I gained a lot of good information. Appreciate it much folks!

    But we never really were able to answer your question about whether it's piped properly or not. We need to see pictures of the boiler and the near boiler piping.
  • Tom ShermanTom Sherman Posts: 6Member
    Thanks SuperTech, I realize I needed much more info in order to get a full understanding...I was just looking more for a general "small pipe to larger pipe" answer and if there were complications in general with that kind of scenario. I realize I can't possibly get a "is it piped properly or not" answer with this one pic. Appreciate your help! Best!...............Tom
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