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How to pipe a Condensing boiler with heat exchanger for non O2 barrier pipe

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Mosherd1
Mosherd1 Member Posts: 76
edited December 17 in Radiant Heating

When using a heat exchanger with a condensing boiler to feed non-oxygen barrier pipe, how should it be plumbed? Option 1, come off the boiler, to a pump, then to closely spaced T’s and back to the boiler, with a separate loop coming from the closely spaced T’s, to a pump, and then through the 80 plate heat exchanger, with then another pump on the isolated side to feed the radiant tubing, or Option 2, come off the boiler, to the pump, through the heat exchanger and then back to the boiler, so basically plumbing it like the heat exchanger is a hydraulic separator?

Comments

  • hot_rod
    hot_rod Member Posts: 26,532

    It can be this simple. You need expansion and relief valves on both sides of the hx

    If the tube side needs glycol, conditioner, or occasional flushing, use some purge valves like the Webstone with hose connections. Counterflow through a FPHX.

    A DirtMag for sure on the tube side of the HX.

    Was the HX sized? Or is the 80 plate a guess?

    Screenshot 2025-12-17 at 12.18.34 PM.png Screenshot 2025-12-17 at 12.21.09 PM.png
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • mattmia2
    mattmia2 Member Posts: 15,444

    if the hx is the only thing on the boiler then there is nothing to separate, just need enough pump to produce enough flow through both the hx and the boiler.

    GGross
  • kcopp
    kcopp Member Posts: 4,614
    edited 1:19AM

    What is the Non- Barrier piping? Poly B, Onix? Regular pex?

    One way is to use an All Stainless Steel Indirect water heater. Use the coil (1" coil at least) and have that as your boiler loop. Then use the hot and cold as your system loops. Use all brass, copper or stainless parts on that side for best results… a good inhibitor after cleaning/ flushing.

  • nate379
    nate379 Member Posts: 149

    Mine has been running since 2015 without any heat exchanger and no issues, so dunno.

    There's not much regular steel, if any, in a combi boiler.

    mattmia2
  • mattmia2
    mattmia2 Member Posts: 15,444

    look at the manufacturer's instructions. a lot of mod cons are copper and stainless so they might do ok on an open system

  • hot_rod
    hot_rod Member Posts: 26,532

    If the pumps are stainless and the expansion tank a lined type likw the the Amtrol Pro you could get all non ferrous piping.

    Connecting Viessmann boilers to non barrier tube voids warranty, possibly others?

    Temperature has a lot to do with O2 ingress. Higher temperature fin tube for example really pull in O2.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    GGross
  • rick in Alaska
    rick in Alaska Member Posts: 1,513

    I wonder how much water quality in different parts of the country affect that.

    I had at least 4 customers who had PB tubing hooked up to their cast iron boiler, and with all iron parts, that had been in for at least 35 years that I know of , with no problems except leaky manifold connections. This was on a radiant system, and with 4way mixing valves, so I'm sure the low temperature of the system helped. I would have thought the pumps would be more prone to scaling up though, but didn't see it.

    Rick

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