Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

anti freeze in closed loop

DD_5 Member Posts: 36
I'd like to add anti-freeze to my systems...(closed loop, backflow preventer at boiler feed so it won't mix with potable under any circumstances). I'm assuming that you can no problem as long as its the same that I've used in solar systems i.e. food grade glycol... Dow .

What is the preferred ratio of glycol to water?

Any other tips or precautions on this? I know glycol doesn't transfer heat as well.
Double D


  • Slimpickins
    Slimpickins Member Posts: 323

    Personally I wouldn't use glycol on any system unless there was exposed pipe and if I do I always recommend an Axiom Pressure Pal MF200. It will save you a ton of headaches.
  • Ironman
    Ironman Member Posts: 6,856

    If you have a aluminum block boiler, You must only use what is approved by the manufacturer.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • hot_rod
    hot_rod Member Posts: 16,093
    determine the lowest

    temperature (burst temperature) that you need to protect to, then blend accordingly. If 35% is enough don't go any richer, as you take additional pumping and heat transfer penalties.

    Make sure the system is cleaned and flushed first. Use a hydronic cleaner if possible.

    If you are planing to blend the glycol use a good quality water like DI or DM (deionized or demineralized). Not RO or distilled water.

    Remove any fill system connected to your water supply, install a LWC device.

    A glycol fill system or a homemade pig are a good idea to makeup fluid for any air that purges out as the system warms and circulates.

    I'd second the advise of not adding glycol unless it is absolutely needed.

    Dow, Nobel, Rhomar, Hercules are some of the quality brands I have used. The HD fluids have a stronger inhibitor package.

    If you have ANY aluminum components in the system use an AL or multi metal blended glycol and keep an eye on the ph level, yearly.

    Stay away from the bargain priced products they may have a weak inhibitor package.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
This discussion has been closed.