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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!

An anode in use for seven years is compared to a new one

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:

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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