Anode rod life, qty, and tank size correlation

The Tank Anode rod life, qty, and tank size correlation

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  • #26738
    redcenter
    Participant

    Will an anode rod last longer in a 30 gallon tank vs a 75 gallon tank?

    If so, is it due to less water reacting to the anode rod or less surface area (the tank) to protect or both?

    So if I add an anode rod to a 6 year water heater can I expect the anodes to last twice as long?

    What if I add 2 anode rods to a 6 year water heater? Can I expect the anodes to have triple the life span?

    Or can the additional anodes only increase life by less than 100%? Say maybe 50-70% more life per additional anode?

    #26739
    Larry Weingarten
    Participant

    Hi, There isn’t hard data I know of on this. I do have lots of field experience though. An anode will last longer in a smaller tank because there is less internal tank surface area to protect. That assumes the condition of the glass lining, temperature, and the water is all the same. I don’t think we can expect twice the anode lifetime with two anodes as the tank will likely be getting better protection. Even with two rods, the tank should be flushed of sediment and T&P checked far more often than every five years. There aren’t many cases where a third anode can be added and I’m not sure it would be very helpful. Think of anode protection like this. The anode is a light bulb and where its light shines is protected. Having multiple “lights” on the same area might not do much good. The real test is to  come back in two or three years and see how much anode is remaining. This will allow you to know how often the anodes will last, assuming water quality doesn’t change much. That help?

    Yours,  Larry

    #26740
    redcenter
    Participant

    Thanks for your thoughts.

    I assumed you would get twice the anode lifetime or close to it because that is how WH manufacturers calculate their warranty, 6 years and 12 years depending on if it has 1 or 2 anodes. It may not double the life but I’m guessing increases lifespan by at least 50%.

    Assuming the above statement is correct, that is why I wanted to add a third anode to the water heaters, even if it means less of an increase of lifespan per anode; as long as the total length of protection increases by a few years I will be satisfied.

    I will be installing several water heaters in a tough to access/maintain location and may experiment with 2 anodes vs 3 anodes in them. I will need to figure out how to document it though. They would all have the same water quality, storage location etc. so it would be a great opportunity to document a test.

    #26741
    Larry Weingarten
    Participant

    Hi, Often the second anode manufacturers install is not as long as it could be, nor as big in diameter as could fit. Actually, the primary anode also is often pretty skinny! I’d check what’s there in your new tanks and install the largest diameter and longest anodes that will fit. This gives you the most magnesium, which is the goal if checking them periodically will be hard. A side by side test would be very interesting!

    Yours,  Larry

    ps. A powered anode might be a good solution to not being able to check rod condition. Powered anodes can fail also and need to be looked at periodically, but it’s another tool you could use here.

    #26743
    redcenter
    Participant

    Thanks for the thoughts.

    In a lowboy/short water heater (electric), if I add the flexible anode rods that are for example 54 inches to a 30 inch tall water heater, can I let the anode just sit on the floor of the tank so I can take advantage of the extra anode length for protection?

    Also, some say aluminum anode rods don’t wear quick enough to protect the tank so that’s why even with replacing them on time the tank will eventually rust out. Is that true?

    If I add additional aluminum anodes and/or extra long flexible anodes will that increase the protection to the tank and maybe stop corrosion instead of slowing it?

    #26744
    Larry Weingarten
    Participant

    Hi, The ideal anode would be a ball in the center of a spherical tank. Letting an anode sit on the bottom of a tank might help or might do very little. I’d use magnesium anodes that are as big in diameter as can fit into the port, and reach within a few inches of the bottom. I’d start with two solid rods and check them in some years… depending on the conductivity of the water. You only need to pull a rod up a little to be able to see how it’s doing. It would be nice to see the whole thing, but it doesn’t have to come completely out.

    The aluminum vs magnesium question depends on the conductivity of the water. I prefer magnesium always unless the water is fairly conductive and you know you will never drink the water, like you might find in a laundry facility. Do you know how hard your water is (in TDS)? Is it softened?

    Yours,  Larry

    #26745
    redcenter
    Participant

    The flexible anode I am referring to would be just 1 of the 2/3 anodes in the tank. So it would be an additional anode to help stop corrosion.

    Magnesium rods wear out quicker so if I was going to put those they would be gone sooner than aluminum ones. So the question is if I put 3 aluminum rods can I avoid swapping anodes to last longer overall vs magnesium; and could I leave the flexible anode hanging in the tank but also the remainder/extra length against the floor.

    It is city water I am assuming hard.

    #26753
    redcenter
    Participant

    Seems like the site was down when I posted my reply above, any thoughts on my response?

    #26756
    Larry Weingarten
    Participant

    Hi, Aluminum could be a health risk, so I play it safe and always replace them with magnesium. Also, aluminum produces lots of gelatinous corrosion byproduct, which doesn’t help. In your case, I think it makes sense to simply use powered anodes, so you are unlikely to have to remove the tanks to check things. By the time you put three sacrificial rods in the tank, you’ve mostly paid for a powered anode that will just keep on going. About the anode sitting on the floor of the tank, I wouldn’t do that. Anodes work like a light as I described above, but they also care about distance. An anode sitting on the bottom head of a tank will do little or nothing to protect the upper head of the tank.

     

    Yours,  Larry

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