Water heaters typically come with magnesium or aluminum anodes. We prefer magnesium. We dislike aluminum for a bunch of reasons. Those are:
· First off, aluminum, being lower on the Galvanic Scale than magnesium anode, produces less driving current between anode and cathode (in this case, the tank is the cathode). We think that means it doesn't do as good a job of protecting the tank, especially in softer waters.
· Second, it produces about a thousand times its original volume in corrosion byproduct, most of which falls into the bottom of the tank as a sort of jelly, and adds to sediment buildup there.
· Third, that gunk also occasionally floats out the hot-water port, appearing as a cottage cheese-like substance clogging aerators and filters.
· Fourth, the rod actually expands as it corrodes so that it is hard, or maybe impossible, to remove one a few months after installation because its diameter is bigger than when it was installed.
· Fifth, along with that, it has a tendency to split off from the core wire, so that chunks fall into the bottom of the water heater, where they stop being anode and start being junk. That also means that if you try to take one out at that point, it may split away from the core wire and snag the underside of the top of the tank, like a fish hook.
· Sixth, the build-up of sediment on the bottom of gas heaters encourages noisy operation, and some people can hear their water heaters loud and clear at night, which is not helpful for those wishing to sleep.
· Seventh. There is a little booklet "The Danger of Food Contamination by Aluminum" by Dr. R.M. Le Hunte Cooper. It details the nasty things aluminum does to the body. The liver, brain, kidneys and spleen seem to be the main repositories, with nervous tissues holding the most by weight. It was written in 1932. Modern plumbing allows some water that came from the heater to be used as cold water. This doesn't matter if magnesium is used in the heater.
· Eighth. If you find yourself ground zero in a disaster, and the water main is broken, about the last thing you want is to be drinking heavily-aluminum-laden water from the bottom of your water heater -- the source of last resort. It could make you sick in dreadful ways: trash your stomach and intestines, create instant arthritis in your joints. No fun!
But all that said, an aluminum/zinc anode is mostly aluminum, although it tends to corrode more slowly than pure aluminum. It is the most economical solution to odor problems if no water-softener is being used. Everything stated here applies to it. So we suggest that those using that anode, or who have bought a heater with a pure aluminum anode, especially if they have a single-control faucet, simply let the cold water run for a few seconds to purge the line of any cooled-off water from the water heater. That's all it takes.
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