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water supply - chlorinated or not chlorinated

josephc Member Posts: 39
My current water supply to my weil-mclain boiler is city water that has gone through my whole house dechlorinator filter by whirlpool. I am going to be running a new pre-filtered supply line to take my lawn sprinklers off the filter so not to waste its service life. Would it be better to also pipe city water with chlorine directly to the boiler or leave it on the supply that has removed the chlorine? The chlorine free water has been feeding boiler last 4 years since we moved in so it has been on straight city water in the past.


  • Gilmorrie
    Gilmorrie Member Posts: 137
    Millions of hot-water boilers have operated successfully on city water that is chlorinated. Perhaps the chlorine is dissipated by the air-removal devices? Not to worry.
  • ChrisJ
    ChrisJ Member Posts: 11,549
    The chlorine is corrosive even when it's released from the water. My steam boiler runs straight city water but I don't have much choice.

    My question is what downsides if any are there to do the "dechlorinated water"?
    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
  • Jamie Hall
    Jamie Hall Member Posts: 15,748
    Chlorine gas is corrosive. The amount of free chlorine or chloramines in city water is not. Some people object to the smell in a heavily chlorinated water supply (try St. Louis in the summer...) but it's not harmful -- either to you or your boiler.

    It is harmful to your aquarium fish.

    On the downsides of dechlorinating. Remember what the chlorination is for: to protect against bacterial and viral contamination of the water and thus to protect your health. If there is no source of bacterial or viral contamination on the dechlorinated side of a water supply, there really isn't much of a downside -- but that assumes that all of your plumbing is up to code (including vacuum breakers, air gaps, or RPZ backflow preventers on all sources of contamination, such as but not limited to... garden hoses. "telephone" showers. Extendible kitchen faucets. Automatic ice makers or refrigerator chilled water spigots. Etc.) Further -- if the dechlorinating filter is activated carbon, as a lot of them are, remember that it is a pretty close to ideal medium for bacterial growth as well, and change it often -- weekly to monthly, depending on the filter, is not too often.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 14,757
    Chlorine really doesn't stay in the water very long, chloraime (chlorine and ammonia blend) does stay longer but also dissipates after some time. I doubt either would cause harm to the boiler or piping.

    I just attended a webinar about this as they are starting to open buildings that have been vacant for the last few months and are worried about legionella growth due to lack of water turns and the the chlorine no longer protecting the piping.

    Usually folks strip the chlorine due to odor and taste, for consumable water.

    I'd check the Ph of the water, steam boilers like it towards the alkaline side to give the metals some protection with a protective layer.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Jamie Hall
    Jamie Hall Member Posts: 15,748
    Good point about the vacant buildings, @hot_rod -- I'd want to run a very thorough flush of every unused fixture in such a building -- particularly things like drinking fountains! Running each one until I did get a chlorine residual. Both hot and cold. If it's on well water, shock the well with chlorine and do it that way.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • PMJ
    PMJ Member Posts: 1,089
    My boiler has run on Cleveland city water for 63+ years. In its earlier years in the 1960's and 70's word is they had to put in 10+ times the chlorine they do now to treat that Lake Erie water. Only one data point but I think a pretty decent test showing chlorine is not a concern.
    1926 1000EDR Mouat 2 pipe vapor system,1957 Bryant Boiler 463,000 BTU input, Natural vacuum operation with single solenoid vent, Custom PLC control
  • gerry gill
    gerry gill Member Posts: 3,004
    Hot Rod probably has the most valid point in that your focus should mostly be on the water’s PH level.
    Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.

  • The Steam Whisperer
    The Steam Whisperer Member Posts: 653
    I would be very careful when starting up the water systems in buildings that have been sitting. Whomever is doing this work should be wearing a respirator and only opening up the valves to very low flows on sinks, tubs, showers etc and keep the lid down on toilets to prevent fine spray from becoming vaporized. The other thing to watch out for is there can be a build up of hydrogen gas in the lines, so when the system "burps" those gases are highly flammable. Don't be smoking a cig when bring the system back on line!
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • motoguy128
    motoguy128 Member Posts: 347
    From what I gather, PH and hardness are the biggest issues. Tank type Water heaters and boilers last forever in my city because they keep the PH above 8, close to 9 when I’ve tested it. Seen plenty of 40+ YO water heaters. The cheap 6 year $300 electric water heaters will last 20 years easy.

    I suspect It’s to protect older piping and the river it’s drawn from might naturally be alkaline due to limestone deposits and clay.
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