Non- O2-barrier PEX and cast iron pumps

Discussion in 'HVAC Heating & Cooling' started by Darent, Oct 24, 2010.

  1. Darent

    Darent New Member

    Oct 24, 2010
    Boston, MA
    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!

    System is in vacation home, cold climate, freezing is a problem.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    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 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.
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  4. Darent

    Darent New Member

    Oct 24, 2010
    Boston, MA
    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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