What you'll find on this page: If most people have never heard of sacrificial anodes, then powered anodes are even less well-known, much less understood. But they've been around for awhile.
Sacrificial anodes are what the manufacturers use in nearly all their water heaters. They are inexpensive, have no parts to break, require no electricity, and last a long time in normal water. The way they function is, when the tank is filled with water, an anodic-cathodic reaction begins between exposed tank steel (the cathode) and anode. Ions are flowing from anode to steel, protecting the latter while the anode rod is slowly consumed. When there is nothing left of the anode, the tank steel starts to rust.
A powered anode -- the technical name is impressed-current anode -- does it differently. Ions are still flowing from the anode, which is really an electrode, to tank steel, but they come from an AC outlet instead of a sacrificial reaction. One such is pictured above. Because of this, powered anodes don't get used up. However, being a manufactured device, the possibility exists for them to break.
Impressed-current anodes have wide industrial uses and anybody who googles the word can find a bunch of them. But they have been used relatively rarely in water heaters. At this time, A.O. Smith uses them in a few of its high-end heaters.
Because they can break and are expensive, powered anodes are not such a bargain for regular water heater situations. And they do require the power to be on to function. In an outage, they stop working, although most outages don't last long enough to damage a water heater. It takes months without a functioning anode before a heater rusts enough to leak.
But if people have odor and are using a water softener, powered anodes come into their own. Most softeners exchange salt for hardness and the salt makes the water more conductive. Sacrificial anodes work harder and are consumed more rapidly than normal. If there are sulfur and anaerobic bacteria present in the water, they also can create smelly water. The powered anode works only hard enough to protect the water heater from rusting and doesn't usually generate any odor. It's not an odor eater or bacteria killer, however. It just doesn't cause the odor problem as it functions. Because the ions in the anodic/cathodic reaction are not generated in a sacrificial reaction, the powered anode doesn't get used up. So the danger is lessened that the homeowner will forget to check the anode often enough and have the water heater rust out.
For those reasons, the powered anodes we sell are the most elegant and economical solution to smelly hot water and to premature tank failure caused by water softeners. Every situation is different, but we've talked to people who went through a new water heater every couple of years using a softener. Anyway, other solutions to odor that we know work are Rheem's Marathon plastic-lined electric water heater, and tankless heaters. Both are far more expensive than the powered anode. Other possibilities include UV systems and well chlorine injection. We are less certain about those, but they may work sometimes. We only hear from the people for whom they failed.
What should you buy? Well, we've created a buying guide for that. Have a look.
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