Water Heaters 101 > Replace Sacrificial Water Heater Anodes to Extend Tank Life

What you'll find on this page: Most people have never heard of sacrificial anodes, even though they have been a key to water heater longevity for decades. This may be the single most important page on this site. It won't take you too long, so read these words even if you skip everything else! Worth noting: the shipping calculator works well for one or two items, but exaggerates if you buy a bunch. For instance, a recent order of six items generated of $53, when the true shipping was about $18. When this happens, we always refund the difference. If you didn't know that, it might scare you off.

The Hidden Ingredient

The single most important factor in whether a water heater lives or dies is the condition of its sacrificial anode. For more than 60 years, it has been used as a key part of the rust protection of a tank, although few people know it's there.

This is a rod made of magnesium or aluminum that's formed around a steel core wire and is screwed into the top of the tank. A six-year-warranty residential tank will have one, while a 12-year-warranty tank may have two, or an extra-thick primary anode. Commercial tanks have from one to five. Special aluminum/zinc sacrificial anodes or powered (impressed-current) anodes can be used to resolve odor problems caused by bacteria in some water. But if you have a vacation home where the water heater sits idle for long periods of time, using them may not be a solution. Click here if that is an issue.

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When the tank is filled with water, an electrochemical process begins whereby sacrificial anodes are consumed to protect a small amount of exposed steel. Powered anodes replace that process with electricity and are not consumed.

When two metals are physically connected in water, one will corrode away to protect the other. Sometimes that's bad, but often it's good. Although many people haven't heard of this, the principle is used all over the place -- anywhere that someone wants to protect metal exposed to water. In marine applications, anodes are known as "zincs" and are usually made of that metal.

All metals fall somewhere on the galvanic scale of reactivity. When two are placed together in water, the "nobler" -- or less reactive -- one will remain intact while the more reactive one corrodes. When steel and copper are together, steel will be the one that corrodes. Indeed, steel is more likely to rust in the presence of copper than it would have been by itself. That's why dielectric separation is necessary on items like copper flex lines when they're connected to steel pipe nipples.

Magnesium and aluminum are less noble than steel, which is why they're used for anode rods.

Remember, the anode is screwed into the tank. That means it can be unscrewed and replaced.

A sacrificial anode's life depends on the quality of the water, the amount of use the tank gets, the water temperature, and the quality of the tank -- meaning how well it was constructed. When salt is added to the water (as in softened water), anodes can corrode more quickly. Water softeners help reduce sediment, but anodes can corrode in as little as six months if the water is over-softened. Do not soften to zero. Leave 50-120 ppm of hardness. This may require some plumbing to add unsoftened water to softened water.

People occasionally ask us if pipe-seal tape applied to the threads of the anode blocks the electrolytical reaction. Tanks we've serviced repeatedly usually have corroded anodes. We've tested with a multimeter and found continuity between the anode and the tank, despite the tape.

While we generally advocate putting two anodes in a tank, that may not be a good idea if you have odor problems. Doubling the anode surface area may worsen odor even when special aluminum/zinc anodes are used that reduce or eliminate the odor.

If you have odor and soften, or for that matter, merely if you soften, consider getting a powered anode that replaces the sacrificial reaction with electric current and isn't consumed through use.

As to which brand has what, we can help you with that. Consider buying a consultation and giving us your details. If we recommend a product and you buy it within 10 days, we'll refund the consultation fee.

Why We Don't Like Aluminum Anodes

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, 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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