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Thread: Non- O2-barrier PEX and cast iron pumps

  1. #1
    DIY Junior Member Darent's Avatar
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    Question Non- O2-barrier PEX and cast iron pumps

    Hello,
    I have PEX without O2 barrier in the cement slab (zone1) and baseboards (zone2). Its a 2 zone closed heating system. Baxi Luna is the heat source, mixing valve to drop temp for radiant, two Taco IFC cast iron pums; each pump in each of the zones. System was installed this spring. This will be the first heating season. Radiant water temp will be about 100 deg. baseboard 170 deg.
    I did not realize at the time when plumber finished/was paid that the cast iron pumps are not optimal for the no-O2-barrier PEX system (He was a young kid, did not know any better?).

    The question is: will/how soon the pumps will fail, should I run system as is until pumps fail or install bronze or stainless steel pumps now.

    What should I do? Thanks!
    Daren

    P.S.
    System is in vacation home, cold climate, freezing is a problem.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    What kind of boiler heat exchanger do you have? O2 in your circulating water can kill lots of things, not only pumps. If there is a risk of say power outages, or you want to shut the system down, you can add antifreeze to the circulating water...you may need to run it a little warmer, as the antifreeze decreases the heat transfer. With the tubing embedded in concrete, you may not get much O2 migration - it is the exposed areas that would be the bigger concern.

    Not sure about the longevity, or the best approach. See what other comments you may get.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY Junior Member Darent's Avatar
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    Thanks for the response.
    Burner is: "Nickel-chrome stainless steel (AISI 316L) primary heat exchanger, high resistance to corrosion, no internal welding, large heat exchange surface and low heat inertia". (Heater is "baxi luna ht 380".)
    I can add antifreeze to the system, system is plumbed to to this. There is almost no PEX outside concrete, I estimate maybe ~30 inches total length. it transitions to copper in the boxed out slab area.
    I was thinking about not using antifreeze, but installing a freeze alarm. the house would call me when there is a power outage or temp falls below 45F in the house....

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