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Mixing steel and cast iron - need inhibitor?

crobar Member Posts: 4
I am adding some steel panel radiators to the existing cast iron system and was wondering if a corrosion inhibitor or other additive is necessary. If so, any suggestions on type and/or brand? I've seen some that are for glycol systems (Cryo-tek) but my system currently uses plain water, so I'm not sure if that would be compatible. Thanks for any information.


  • kcopp
    kcopp Member Posts: 4,390
    Any Hydronic heating system can benefit from a good cleaning w/ a cleaner like Fernox, Rhomar or Sentinel.
    Same goes w/ the inhibitor.
    This is especially true if you have plastic tubing that feeds the radiators.

    If you have plain water in the system why add glycol?
    Unless there is an eminent freeze risk I avoid its use...period.

    It is important to clean the system well before the adding glycol as the inhibitor in the glycol will be compromised if just adding it to a dirty system.
  • hot_rod
    hot_rod Member Posts: 21,841
    It is always a good idea to clean and add an inhibitor.

    First check the fill water quality, ph, hardness, TDS. Most of the boiler and indirect manufacturers will give you a range for those.
    it really applies to any component in the system including the panel rads, pumps, control valves, etc..

    Fill the system, purge, flush, check for leaks.
    Add the cleaner per can directions, run up to temperature. the cleaners in their basic form are soaps, so warm water works better than cold.

    Flush all the cleaner out, some brands include test strips to assure you have it all flushed properly.

    Refill the system with good quality water, buy some or run through a DI cart if the site water is not up to snuff.

    Ideally you will check the fluid condition yearly, or every several years at least.

    The inhibitors provide multiple functions.

    They are a film provider to coat all the cleaned metal surfaces.
    They have an O2 scavenger to assure no O2 is left to support corrosion.
    A ph buffer
    The yearly check is to assure the inhibitors are still up to snuff.

    Several companies offer these kits, good for about 25 gallons. Or buy bottles and pump it in.

    I like the Rhomar products, they have done a lot of multi-metal testing and development. Their kit has a nice connection fitting to screw onto a boiler drain cock or any hose thread in the system. It's just hitting the shelves.

    It does add a bit of additional time and $$ to a job, multiple trips, but it is a protection for your systems, to assure a long life and good operating conditions for heat transfer.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream