A residential 17 year old electric water heater is working well in Florida. Maintenance is overdue. I plan to inspect / replace:

  • sacrificial anode (expected to replace)
  • heating element (expected to replace)
  • flush the tank

With regard to purchasing a sacrificial anode, there seems to be at least two features one must decide:

  1. Metal type: magnesium, aluminum or aluminum/zinc alloy.
  2. Length

How does one decide on proper metal to use and the length of the anode? As it understand it, the threading is standardized.

There is plenty of space above the tank for a long rod, so a segmented anode is unnecessary.

2 Answers 2


Magnesium > Aluminum

Aluminum anodes have a few issues:

  • Aluminum anodes tend to swell and break up as they are consumed, aggravating sediment and raising blockage potential
  • Aluminum in our bodies is...not the greatest thing in the world
  • If an aluminum anode passivates, it may be very difficult to tell what is going on
  • Aluminum anodes can be difficult to replace due to the aforementioned swelling blocking them from exiting the tank
  • Aluminum anodes also may be less effective due to aluminum being a less reactive metal than magnesium

All of this adds up to a magnesium anode being a superior product any time you aren't encountering rotten-egg odors due to sulfur-reducing bacteria in the tank. (If you are getting rotten-egg stench from a regularly used tank, then you'll need to switch to an aluminum-zinc anode, or a powered anode if that doesn't fix it.)


I go with zinc because aluminum swells more and when aluminum breaks down it can plug flow restrictor and ariators. you will need the model number of the water heater to get the correct length. I find solid rods last longer I have segmented break at the joints several times. In 1 home I installed an electronic annode it was very expensive almost 200$ but that home had very soft water and standard annodess were almost gone in 1 year I never had to replace the electronic one and it was still going strong after 10 years.

  • Was the $200 anode installed in Florida? or environment with similar water?
    – gatorback
    Jan 7, 2019 at 14:56
  • 1
    It was in oregon, it was the only home I have had with soft water, the soft water really eats the annodes quickly, I would not change the heating element if it measures good, I have had elements last the life of the tank and have also had elements only last a few years so I keep a spare because they are easy to replace but I only change them after they fail. I do flush the tank and check the annode regularly at my current home the annode life is 4+ years. So the return on an electronic annode would not be worth the higher cost.
    – Ed Beal
    Jan 7, 2019 at 15:35

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