Aluminum Versus Magnesium Anode

In determining, which is better, aluminum versus magnesium anode rods, we must first examine their function in a water heater. Examining their durability, function, and how they’re used all factors into determining which is the best to use for a homeowner’s tank-based water heater.

Aluminum Versus Magnesium Anode

Some anode rods prevent water tank corrosion, with experts often referring to them as the “sacrificial anode.” Tank-based water heaters experience a higher level of corrosion due to the water’s acidity and the heat produced by the tank itself. This causes the anode rod to corrode before anything else is found in the water heater.

When an anode corrodes, it sends electrons directly into the water tank, which prevent the heater from rusting. The process is called electrolysis. It occurs when two pieces of metal are placed in water such as an anode and steel water heater. The anode corrodes because the less reactive metal (anode) will disintegrate more over the more reactive metal (steel water heater).

The anode rod corroding before the water heater means that the heater will last longer. However, the anode rod will require replacing. Rods are replaced every three-to-five years. However, how fast they corrode may depend on other variables.

If the anode is not replaced, and/or is fully rusted, it will fill the water heater with rust. This will cause the heater to slowly fail. The cost to fix it can be substantial, and in some cases, a new water heater may be required.

Aluminum Anode Rods

Built from aluminum, these anode rods react the slowest with water elements. They emit a low voltage during electrolysis, which slows down the corrosion process. The pace at which corrosion occurs depends on the water condition. Most tank-based water heaters contain aluminum anode rods.

If there is a limited space, companies will use flexible aluminum anodes. These are created to fit when straight ones are unable to. They are placed directly into water heaters that are in areas where there is a low ceiling, basement, beneath stairs, closets, or attics.

Fixing the anode requires bending the flexible sections as they’re placed into the water heater via the opening at the top. Make sure the aluminum anode is not in contact with the inner parts of the heater.

Aluminum anodes are ideal where the water contains sulfates. They are better at changing sulfates into hydrogen sulfides. Aluminum anode rods are preferable in this case as magnesium anodes will only increase the hydrogen sulfide compound. It will end up creating a foul, rotten egg smell.


  • Cost-effective
  • Include aluminum and alloy of zinc, which increase strength
  • Extended life span
  • Get rid of strong smells when water contacts metal


  • Can cause plumbing issues if rust falls off into taps/water
  • May cause sediment buildup in the tank if not regularly maintained
  • Water filters/tap aerators can clog from sticky byproduct
  • May disconnect from core wire
  • Expand as they corrode, making them difficult to remove
  • Deposits are damaging to spleen, brain, liver, and kidney

Magnesium Anode Rods

Magnesium anodes protect the inside of the heater from corrosion. They divert the corrosion process to themselves. Therefore, they have earned the title “sacrificial rods.”

Magnesium rods are used in places that have soft water, and they only last a short duration. They are more reactive over aluminum anodes and provide a higher voltage.

Even though they wear faster, they do have health benefits when they are dissolved in water.

Screw-in applications and in-line cold water installations benefit from this type of anode. Water high in pH produces scale in a water heater. This makes the water high in alkaline. They are a suitable alternative, in this case, and are useful when water contains higher levels or chlorine and chloramines.


  • Provide superior corrosion protection
  • Dissolved magnesium has health benefits


  • More expensive
  • Can cause hydrogen sulfide reaction which smells like rotten eggs

Aluminum Versus Magnesium Anode Rods: Which is Best?

In selecting the best anode for your water tank, the deciding factor becomes the water’s level of hardness. Harder water requires an aluminum anode rod. For areas with soft water, a magnesium anode rod will work best for your system.

While aluminum anodes are cheaper than magnesium ones, the magnesium rods tend to need more replacing.

When to Replace an Anode

Anodes require replacing when the following occurs:

  • Water heater makes popping or loud noise while heating
  • The water tank is over five years old and has never been changed
  • Slimy gel when cleaning faucet aerators
  • Water tank smells like rotten eggs
  • Anode looks completely corroded

One of the detriments of an aluminum rod is the corrosive product formed on the anode over time tends to harden. When this happens, it sinks to the bottom of the tank. There is a potential for this material to get into the taps and cause future issues.

When to Replace an Anode

While aluminum anode rods are commonly used, they do have a variety of issues associated with them. From plumbing issues, problems with rust, and potential health concerns, homeowners should be weary of using this product.

They are beneficial when used with hard water. However, customers should be mindful to properly maintain their water tank. Corrosion easily occurs and can lead to a buildup of deposits within the hot water tank. This sediment can easily leech out into the water supply. If it doesn’t cause health problems, it will cause issues with the taps.

Therefore, proper maintenance is crucial to the homeowner’s well-being.

Magnesium anode rods may be more expensive and may require frequent replacing. However, they are more of a sacrificial rod. This means that the corrosion process is diverted from the water tank to the anode.

They have less issues than the aluminum anode rod, and when dissolved, they do not produce any harmful health effects. In fact, they offer health benefits, instead.

Most experts feel that magnesium anode rods are the preferred choice because they lead to fewer health issues and do not contribute to plumbing problems.

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