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I'm trying to decide where to place my water softener. I originally planned to put it in the utility closet where city water comes in, but this plan had a variety of issues.

My current plan is to re-route cold water going into my (conventional) water heater so that it goes through the softener first. Is there anything I'm not anticipating with this plan? Is there any reason not to route the supply to the water heater as shown below?

The water softener will be in a laundry room with an easily accessible drain. I plan to run Pex through the ceiling.

It seems like a simple approach, but I'm not a plumber so my weakness is not knowing what I don't know.

Schematic

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  • Can we assume you have a conventional, storage-type hot water heater? Or is your hot water heater a tankless type? Sep 12, 2016 at 0:25
  • @ThreePhaseEel Yes, it's a conventional water heater.
    – T.D. Smith
    Sep 12, 2016 at 0:26
  • I would suggest at least editing the title, to make it clear that the given answer is about whether it’s bad to feed a tank water heater with artificially softened water. It would make it easier for people to find an answer to this question, and help prevent duplicates such as mine.
    – Mat
    Sep 29 at 19:43

1 Answer 1

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The main issue with feeding artificially softened water into a storage hot water heater is that softening water makes the water more conductive. This isn't a big deal, except for the fact that the protective anode in your water heater tank that keeps it from rusting away into oblivion works harder and faster in more conductive water. This is because corrosion is an electrochemical reaction, and there is actually a small galvanic current flowing through the hot water in your tank and back to the sacrificial anode through the tank wall -- the more conductive the water, the larger this current, and the faster the "battery" created by the sacrificial anode, water, and tank wall discharges, eating up the anode.

As a result of this, feeding softened water into most stock hot water heaters will cause them to die rather quickly of rust -- the anode goes first, then once the anode's gone, the tank itself proceeds to rust out. If your tank is so equipped, regular anode changes (you may have to change anodes at half the warranty period or less!) are one way to keep the tank from dying; however, a better solution would be to fit the tank with a powered anode -- this uses wall power to produce a small electric current in the tank that suppresses the corrosion reaction by driving it "backwards" if you will. (Think of the difference between discharging and charging a battery.)

(I have no affiliation with the Water Heater Rescue folks, btw -- they simply do a good job supporting something most people don't think about, and that's how to treat hot water heaters as something other than a throwaway device.)

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  • Interesting - wouldn't this be an issue for lots of people with whole-house water softening?
    – T.D. Smith
    Sep 12, 2016 at 0:56
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    @Tyler -- for folks who plumb soft water to their water heater, yes. Sep 12, 2016 at 0:58
  • Never heard of a power anode. What about dieletric fittings/joints? Do they serve the same purpose, and do they need to be replaced?
    – Mat
    Sep 29 at 7:23
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    @Mat -- the tank'll just leak :P Sep 30 at 0:08
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    @FreeMan -- it impacts all water heaters, but yes, with regular anode rod changes, you very well could get 50 years out of a standard tank water heater Oct 7 at 0:47

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