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Thread: antifreeze protection for hydronic heat

  1. #1
    DIY Junior Member fozzy12's Avatar
    Join Date
    Jan 2008
    North of Detroit, MI

    Default antifreeze protection for hydronic heat

    I have a closed system hydronic heating system in my workshop. I want to protect it in case of power failure during the winter months. What type of antifreeze do you recommend? It's not connected to city water, it's a totally separate system. Can I use automotive type antifreeze? I was ready to buy some RV antifreeze when I read the label and it said specifically not for use in hydronic heating systems.


  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Sep 2004
    New England


    Go to a plumbing supply house and get the stuff designed for this. One important thing to note is the addition of antifreeze actually decreases the system's ability to transfer heat - in other words, your boiler will function as a smaller unit when you add antifreeze. Course, it will keep the system from freezing if you have enough in there. I think the deficit is about 10%, but don't quote me on this...one of the pros would know.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY Senior Member zl700's Avatar
    Join Date
    Aug 2009


    The insulating factor for heat exchange can be as high as 25% depending on concentration or level of freeze protection, with the norm around 15-20% reduction.

    Also, heat exchange in the boiler depending on type is effected, many times causing operational problems such as whining and whistling can be heard.

    Proper concentration, flow, adequate radiation and perhaps some burner adjustment and all is well for that peace of mind


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