Dual Anode Question

The Tank Dual Anode Question

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  • #20128
    C-Rex
    Participant

    Suppose water heater A has one magnesium anode that is replaced with a new anode when the first is nearly worn out (at 6 years, for instance).

    Water heater B is exactly the same, except it has two anodes from day one.

    Will one of these water heaters have a longer life from a corrosion perspective, and why?

    What I am trying to get at is what is the advantage of a second anode (from day one). Does it simply get enough magnesium onboard so there is enough for, say, 12 years? Or does the additional magnesium provide increased corrosion protection from day one? On other words, is the “intensity” of the corrosion protection increased, or is the “intensity” the same, it just lasts twice as long?

    #20129
    Randy Schuyler
    Keymaster

    The way you’ve described it, I’d say they’re equal. The main advantage to two is for people who forget their water heaters, which is most everybody. It’s hard to remember six years down the road. That said, I only have one in mine and it’s going strong after 32 years. But I don’t forget.

    Randy Schuyler

    #20133
    Larry Weingarten
    Participant

    Anodes work best in a line-of-sight way. That is, the anode protects best what it can “see”. In a gas heater, the flue makes it impossible for a single anode to see everything equally, so two anodes will provide better protection. Also the more anode metal there is, the longer it will last. So, the answer isn’t all one or the other but a bit of both. 😎

    Yours, Larry

    ps. A perfect water heater would be a sphere, with a ball of magnesium in the center of it. That way, every bit of steel tank would have equal protection.

    #20134
    Randy Schuyler
    Keymaster

    And THAT said, my heater is still 32 years old and never had more than one anode.:P

    I was in a hurry when I posted this. I wanted to elaborate a little. Larry is technically right, naturally.

    We do know that anode protection doesn’t go everywhere. Steel nipples will rust to ruin even though there is a functioning anode in the heater. But most heaters sold have one anode and if you replace that from time to time, they do just fine. I wouldn’t let the two-anode thing sway me from buying a one-anode heater if all the other specs look good.

    Randy Schuyler

    #20135
    C-Rex
    Participant

    Randy,

    How do you monitor the anode? Pull it out and examine every year?

    What different characteristics do you look for in determining if it is time for a new anode?

    Should any precautions be taken so that the threads don’t seize up – so that the anode will unscrew without damaging things? I would guess that if such precautions are taken, they cannot interrupt the electrical continuity from the anode threads to the water heater – correct?

    #20136
    C-Rex
    Participant

    So it is like electro-plating, where most of the current flows thru the least resistance – the nearest portion of the tank. So is the degree of protection proportional to current, or is an area fully protected so long as there is some current.?

    #20137
    Randy Schuyler
    Keymaster

    I’m leaving your second post to Larry; it’s getting a bit beyond my expertise. But yes, you pull it and check it. Maybe every year or every couple. That depends on what the wear rate seems to be. Replace when you can see a total of six inches of core wire anywhere on the anode.

    Use six wraps of Teflon tape. It does not interrupt electrical continuity. Start the nut by hand and when it feels like it’s screwing down, then apply tools. Impact wrenches are only good for breaking loose an anode and perhaps the final tightening. Anything else and you can strip the threads tightening before you know it or have an anodic centrifuge flying around the inside of the tank when loosening. I’ve seen one picture of such a result and it was a mess.

    Randy Schuyler

    #20138
    Larry Weingarten
    Participant

    Hello: There are shades of grey in this. Rheem states that you want to replace the anode when six inches of the anode’s core wire is exposed. To me, that means the protective metal is six inches further from the metal to be protected and I’m pretty sure there is a fudge factor in it. Perhaps one could wait for there to be a foot of exposed core wire. Protection is a combination of water conductivity, distance between metals, surface area of the metals and purity of the anode. The goal is for there to be enough current so the hardest to protect part remains protected. That part is usually the joint between the bottom head and sidewalls of the tank. This is reason to use full length anodes.

    Best is to check the anode at one year old and see how fast it’s being used up. Judge from there how often to change it. 😉

    Yours, Larry

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