Water Heater Anode Rod Replacement

What is a sacrificial anode? How to replace aluminum, zinc or magnesium water heater anodes

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Water heater anode rod or sacrificial anode is the important component part with only one purpose; to protect the metal tank from corrosion. Use this article to learn how to replace the anode, installation tips, how it works, about different types and when to use each one.

Why the anode is important

Most hot water heaters are equipped with one or more anode rods. Anode service depends on the water conductivity as the rod deteriorates over time. This is why it is important to maintain it, to keep the tank in operating condition. Depleted anode rod does not affect the water taste or color but the regular inspection and replacement can extend the life of the heater.

Under normal conditions, the water heater anode rod will be consumed in four to five years and the metal tank will start to corrode. Based on the number of the anodes one heater has the warranty is different. For example, the medium quality appliances come with the most common warranty of five-six years. Models that are equipped with two rods or one large or heavy duty one, are better, as they allow manufacturer to provide a longer warranty (12-years is one the longest I have seen).

If your heater is relatively new, with a several months of usage, and you hear noise like crackling, popping, gurgling, you might have a problem with the anode rod. Smelly water is another problem... Read further to see why.

How does the water heater anode rod work?

Depends on the water hardness, its chemical structure and hot water usage, these heating appliances, even RV water heaters (like Atwood or Suburban) can be equipped with Aluminum, Magnesium or Zinc water heater anode rod. The inside of the anode is made of the steel wire core (stainless steel on better quality rods), while on lower quality ones you won't find the SS material.

Heater tanks are typically constructed of steel. Since metal tank carries water, it has to be protected against the aggressive water action. There are two ways how to defend the tank from the rust: with the anode rods and tank lining.

Inner tank surface is covered with glass or porcelain lining, but complete coverage is sometimes neglected due to manufacturing imperfection or damaged (cracks) as the result of handling and transportation.

On the other side, potable water contains elements like oxygen, calcium, magnesium, is heated inside the tank.

These ingredients are adding water the ability to be conductive or electrolytic, and to allow the electricity to flow through the water and from one metal (anode) to another (cathode). Changing the water structure or type of material (metal in this case), the amount of electricity can be controlled.

Between anode and cathode, two metal surfaces, a low resistance electrical circuit is created, where water acts as a medium, providing the cathodic protection to the inside surface of the tank. This is protective current that keeps metallic ions at the cathodic surface (metal tank) from corroding.

If tank material is anodic than the rapid failure might occur.

anode rod - sacrificial anodesAs the heater tank is cathode, in order to slow down the corrosion, manufacturers are adding another metal element, water heater anode rod. The rod is made with a higher current potential than other metal elements in the heater, to allow galvanic current to flow from the rod.

Water heater anodes are sending electrons to the metal tank and release positive hydrogen and metal ions to the water. During such process the anode rod starts depleting, sacrifices itself to protect tank and extend its life.

This is the reason why it is called sacrificial rod or sacrificial anode.

Note: Created hydrogen gas might form high concentration which is explosive. Special care should be provided for anode replacement replacement and installation.

Once the water heater anode rod is depleted the tank will start to corrode, eventually developing a leak.

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Types of water heater anodes

Magnesium anodes

Standard water heaters are equipped with the magnesium anode rods (identifiable by weld bead on the plug), and they work the best where water is not hard (softer). If the water is hard, magnesium anode rod in hot water heater do not last very long, usually couple of years. Magnesium anodes are used as they corrode at a faster rate than the iron.

Aluminum anodes

For extremely hard water and where conductivity is high, an aluminum zinc anode rod might be a solution.

aluminum anode rod

If you live in the area where the water supply has a high PH (8+), water condition will react with the aluminum anode rod and form the excessive amounts of aluminum hydroxide. Gel like substance will then reside on the rod and bottom of the tank making the above described noise.

Zinc anodes

If you experience rotten egg odor coming out from the hot water tap, which is the most common complaint associated with the anode; one solution to reduce the smell is to install a zinc anode rod. This might be a good solution when replacing already depleted one as it never comes as factory installed.

Zinc anodes are actually aluminum rods with a small portion of zinc. The proportion is 1:10, and zinc is added to fight the sulfur (rotten egg) smell from the water.

If using chlorination procedure to eliminate various bacteria that are causing the odor, remove the rod and bring it back when done.

Note: Removal of sacrificial anode, for any reason will void the warranty and affect the tank longevity.

Flexible anodes

You might also want to consider installing a flexible anode rod in hot water heater since it provides more flexibility. The rod is divided into several smaller sections (links), which makes the whole rod instead of one solid piece, bendable, which would be great if the unit is installed in tight spaces, or there is limited overhead clearance.

Powered anodes

Water heater, such as AO Smith Effex is equipped with the non-sacrificial powered anode, which is a better solution than the above mentioned, since it lasts a life time and provides much greater performance in any water condition. It is plugged into an electrical outlet and since it does not deteriorate it can be a permanent replacement (unless damaged). It is also a fix when using a water softener and have the smelly odor from the heater.

Some manufacturers like Rheem water heaters Co. are producing models (Marathon) without water heater anode rod. In this case metal tank is replaced with plastic.

Anode rod replacement and installation

Sacrificial anode rod life depends on the quality of the water, tank use and its quality. They can last about five years or longer, but recommendation is to remove it every two to three years for inspection. Be careful when using water softeners for sediment problem as it is exceedingly corrosive and the anode rods dissolve faster while reducing heater life.

Water heater anodes are screwed in to the top of the heater with a 3/4" hex head screw. For standard products, with warranty up to 6 years you will see one element, but for heaters with longer warranties don't be surprised if you see more than two.

Note: Hex head can be visible or hidden. If it is hidden it is usually under the plastic cover on the top.

The best time for water heater anode rod replacement is when the steel core is exposed more than 6" either from the bottom or the top; when the middle of the rod is exposed or if diameter is less than half the original size.

Use these steps to replace or remove the water heater anode rod:

  • Shut off the power to the heater.

  • Turn the cold water supply off.

  • Recommendation is to drain out few gallons from the drain valve at the bottom of the heater.

  • Drain the heater using the garden hose and route to the open drain. Open a nearby hot water tap to vent heater for draining. Drain to the point below the outlet connection nipple.

  • Close drain spigot and remove the hose.

  • Remove the water heater anode rod using the appropriate tool.

Removing a water heater anode rod is a simple do-it-yourself home project, where you can use a ratchet wrench to unscrew the old and screw in a new anode rod. Be sure to use Teflon tape on the fitting threads, so it can seal tightly. If only checking, be sure to clean the calcium-carbonate build-up. Buying online is the most convenient way, especially if looking for something specific, like Suburban anode, zinc alloy anode or flexible magnesium anode rod.

(All pictures are courtesy of Amazon.com)