Vital but little known role of anode in hot water heaters

Even though hot water heaters have utilized anodes for over half a century, they and their vital function are mostly unknown. Let’s have a closer look.

What is a Hot Water Heater Anode?


The anode is a piece of metal inserted into a water tank. It is there intentionally to serve as a source of easily sacrificed metal to take part in the chemical and electrical action that heated and flowing water naturally generates. Electricity flowing between differing metals and in fluid with salts and acids (such as water from natural sources or water mixed with water softeners) causes atoms of metal to be carried away with the solution of fluid and salt or acid.

What does an Anode do for a Hot Water Heater?

Since the metals chosen for anodes tend to break down under electrolysis faster than the metal of the tank, the metal of the anode will supply the atoms demanded by the chemical composition of the water; less tank metal will corrode when anodes are used. The number one source of water heater failure is corrosion, so use of anodes measurably extends their life.

Generally, there are two kinds of metals used: either aluminum or magnesium. Though they both function well as anodes when used in steel tanks, they do have different properties.


  • Produces less reactivity than magnesium and will therefore probably not protect the tank quite as well.

  • Produces a large quantity of corrosive by-product, leading to a jelly-like deposit in the bottom of the tank, and may also flow out to block aerators and filters.

  • Expands as it corrodes and often also flakes or splits, which can make it difficult to remove when checking or replacing.

  • Aluminum is more recently considered by some to be a contributing factor in certain health-related issues. For those concerned with such things, though the quantities are relatively small, some aluminum will invariably make its way into the drinking water tapped from the household system, especially, but not exclusively, when using hot water to mix with foods or drinks.


  • Efficient source of protection for the tank.

  • Has no known detrimental health effects.

  • Does not expand as aluminum does when corroding.

Special-purpose alloy of Aluminum/Zinc/Tin:

  • Zinc is a natural anti-fungal and suppresses the growth of bacteria that results in a rotten egg smell in water. This anode is sometimes used where the natural water source has a foul smell.

Replacement of Anodes in Water Heaters is Periodically Required

Because they are deliberately sacrificed in order to protect the steel of the water tank, anodes should be regularly checked and replaced when significantly degraded. Frequency will depend on local water and mineral conditions, whether you are using a soft water system (the salts used accelerate the deterioration of the anode, especially of over-softened), overall use of the tank, water temperature operated at and quality of tank construction.


For any questions, or for help with water heater repair and servicing or replacing the anode, contact a reputable local HVAC service.

Creative Commons Attribution: Permission is granted to repost this article in its entirety with credit to Alley and Co. Heating/Air and a clickable link back to this page.

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