Understanding the Function Anode Rods Play in a Water Heater System

July 1st, 2019

A relatively straightforward set of components inhabit a water heater system. A gas burner or electric element heats a tank filled with water. In a tankless model, it’s a heat exchanger that provides on-demand hot water. Thermostat, heat source, and delivery system, the equipment parts come together. Anode rods aren’t a super-obvious system feature, though. Yet, without any doubt whatsoever, they’re every bit as indispensable as the equipment’s thermostat.

An Active Corrosion Protection Mechanism

Cut to the chase, anode rods exist to extend the life of water heater systems. They actively prevent corrosion by “sacrificing” their own material bases. Screwed into the top of your tank, the zinc-coated baton pokes deep into the water. Somehow, through some kind of fascinating electrolytic process, the exposed steel of the tank is protected from getting rusty. Now, if this was corrosion-protecting finish, there’d be nothing to understand; the galvanized coating would stop the oxidizing effect in its tracks. But there’s no plating on the steel, no expensive heat treatment work or exotic elements shielding the exposed steel. There is, however, that electrolytic circuit, as set up by the anode rod.

A Noble Metal Primer

Anode rods are made of zinc. There are also magnesium variants and ones made of aluminium. Located somewhere on the galvanic scale of reactivity, “noble” metals resist electrolysis when placed in a tank full of oxidizing water. Therefore, if a water system’s steel jacket is currently that circuit’s most reactive element, it’ll rust. To get around this adverse effect, equipment designers install metal rods that are significantly more reactive than steel. Less “noble” than the tank alloy, the anode rod sacrifices itself to save the steel tank. That’s a literal sacrifice, by the way, which is why these zinc, magnesium, or aluminium shafts require replacement every few years. Otherwise, the rod will break down until it is functionally useless.

What if anode rods didn’t sacrifice themselves? What if they didn’t rust quickly and disintegrate? There is such a feature. By providing the tank-inserted stick with a trace amount of electrical current, you can turn the rod into an anode without triggering off that material deterioration process. A powered anode rod can do everything that a non-powered variant can do, yet it won’t rust and eventually crumble. So, one more time, anode rods rust faster than steel. They take the place of the exposed equipment’s metal surfaces in an electrolytic circuit. But remember, less noble alloys require monitoring, for they’re always being eaten away. For maintenance purposes, a three-year lifespan is common. Of course, you could opt instead for a powered anode.

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