Water heater sacrificial anode metal selection

anodewater-heater

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.

Best Answer

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.)

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