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High Chloride Water and Hydronic Heating

TimeBandit Member Posts: 24
The building's water supply has high chlorides (1000ppm+) and high free chlorine (Cl2), as well. To reduce corrosion of metal components (stainless steel heat exchanger, thermisters, etc., in the closed loop hydronic system, it has been suggested to flush the system using TSP, blow it out with compressed air, and fill the system with bottled water.

Question: What kind of water am I looking for? Spring, distilled, ionized, de-ionized, filtered, etc.

Also, glycol may or may not be used... pros and cons for this, too.

If anyone has any feedback on this, it would be greatly appreciated. The more info, the better. Elaborate as you see fit. Thanks.


  • Jamie Hall
    Jamie Hall Member Posts: 17,165
    Any of the

    less expensive bottled waters will do -- Poland Spring, that sort of thing.  You are looking for relatively low salt, of course!  You really don't want ultra-pure water such as distilled -- it's almost as corrosive as what you have, oddly!  In some areas the cheap stuff is available in 5 gallon jugs; certainly in 1 gallon.

    The pros and cons of glycol... well, if there is some thought that the building might be shut down, or you live in a cold climate and the power may go off and no generator, I'd be inclined to use it.  It's cheaper than a frozen pipe.  On the other hand, if you don't have to, perhaps better not to.  Glycol mixes have slightly less heat capacity than straight water, for one thing, and for another if you ever have to take something apart and re-solder it, it's a bear.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 15,066
    how many gallons are you talking

    You can purchase DI or DM water at most water treatment facilities. Check your area for a Culligan. I hauled fill water in a plastic 55 gallon barrel, the local water treatment companies would fill it for me while I waited.

    The more they strip from the water the more aggressive it can become. RO or distilled is expensive and overkill. Even DI or DM may need some hydronic inhibitor added depending on the metals in the system. Check the ph of the fill water.

    For large systems requiring hundreds of gallons you can rent DI equipment. It looks like a large softener tank, but no brine backwash. After so many gallons flow through it, they re-bed the tank. Culligan is one source for rental DI units.

    If glycol is the final answer, buy it pre-mixed and the dilution water is no longer needed. depending on the temperature protection desired you may get by with 35% glycol.

    Sometimes the pump sizes need to be increased when you add glycol, it's harder to circulate, especially cold.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • TimeBandit
    TimeBandit Member Posts: 24

    Good info, thanks a lot.
  • ChrisJ
    ChrisJ Member Posts: 11,985
    Distilled water

    Jamie, do you have a link to anything explaining why distilled water would be more corrosive than normal water? I cannot find anything and am concerned. Also, different system but 99% of what steam radiators receive is distilled water and they don't seem to have any problems with it.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • conversiontime
    conversiontime Member Posts: 87
    distilled = corrosive

    Chrisj, I recently spent one whole night researching this issue prior to DIY coolant change on car due to so much debate and decided that basically, yes, distilled is more corrosive to metal in pure form vs "natural" water be it hard or soft. In coolant/antifreeze mixes distilled is still recommended b/c coolant itself is corrosive and has additives to slow the process. These additive slow the entire corrosion process across the mix and so therefore most car experts recommend a 50/50 mix of distilled and coolant vs 50/50 of tap/well that may or may not have high mineral loads (scale kills car radiators too).

    So while I was not looking specifically about steam and hydronic heating systems, I did see numerous mentions by various heating contractors to avoid pure distilled water in hydronic or steam applications b/c of corrosion issues. But others claim it is fine and that mineral deposits/scale are what really rot boiler fast. There have been a fair amount of threads here over the years and no real consensus that I noted. I would be inclined to not worry about it, especially since it sounds like you add a fair bit of water over the season, I assume this is via pipe supply and not distilled?
  • ChrisJ
    ChrisJ Member Posts: 11,985
    edited January 2014


    I've found the most I'll add is around 1/2 gallon if it's been a really cold month. More typical months is closer to 1/4 gallon a month.

    Yes, I feed city water.

    I'm curious why more radiators don't rott out if distilled water is corrosive. Unless it's because of how thick they are. I checked the TDS of my return water a few times and found it to be around 2ppm by the time it got back to the boiler.

    Please understand I am in no way saying you or Jamie are wrong. I have no idea.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • conversiontime
    conversiontime Member Posts: 87

    From my simple understanding metals like aluminum, zinc, copper that get corroded quickly in distilled water. I believe black pipe corrodes slower but most literature focuses on other metals.
  • ChrisJ
    ChrisJ Member Posts: 11,985
    edited January 2014

    Based on reading this alone it seems to be very true. This link isn't about distilled water alone but it does talk about it.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • TimeBandit
    TimeBandit Member Posts: 24
    good info

    Thanks to all of you for contributing. I have been researching it myself, and, between my research and the feedback here, this is what I gather: DI or DM water should be used, or just regular bottled spring water. RO water is too expensive to be considered (and too pure), and distilled should only be used if it is mixed with glycol/corrosion inhibitors. Sound about right? Thanks, again, everybody.
  • SWEI
    SWEI Member Posts: 7,356
    RO water

    is less expensive and less corrosive than DI water.  We regularly blend it with tap water to get optimal TDS and hardness levels.  Remember that calcium and magnesium are both buffers.