An anode rod is a rod made of “sacrificial” metal. Like batteries, the anode produces an electrochemical reaction in the tank. The anode slowly wears away instead of the lining of the tank. As long as the anode is present and functional, almost all corrosion or rusting on the tank’s lining is prevented.


To all consumers who are shopping for a new water heater, an important aspect of the new appliance is the accessibility to its anode rod. On top of the water heater is a part called a hex head. It is either visible or not. If it is not visible, the hex head is either located underneath the sheet metal top or is connected underneath the hot water outlet. You shouldn’t have to settle for a hard to find anode rod. I recommend not purchasing this water heater. Look for a water heater with an easily found hex head.

In the case of commercial water heaters, the outer sheet metal top of the water heater must always be removed for access to the anode rod. The hex head is rarely found exposed, whether it is an electric or gas heaters. As you remove the top to the heater, mark the top of the heater itself so that assembling it together later will be easier. At this point the hex head for the anode rod can be found easily on any commercial electric heater. On gas heaters, the hex head will probably be easy to find if it has a single flue vent. If it has more than one flue vent, it may will be more difficult to locate.


An anode is made out of aluminum, zinc, or magnesium. It is formed around a wire running down the center of the rod. Hard water areas of the country often have water heaters with aluminum rods installed because aluminum is the best material for hard water conditions. If your anode rod has deteriorated down to the wire or is gone completely, this is usually a sign of hard water. Be careful of aluminum anode rods, however. Science believes that there is a link between aluminum in the diet and Alzheimer’s disease. Do not drink or cook with hot water from a tank which uses an anode rod made out of aluminum. To determine if you have an aluminum anode rod, remove it, then bend it. If it bends easily in your hands, it is probably made out of aluminum.

Combination Anode

Usually anodes are installed with 3/4 in. hex heads screwed in the top of the tank. However, a combination anode is attached to the hot water outlet pipe nipple, also screwed in at the top. All water heaters have a minimum of one anode rod. Some water heaters have longer warranties because they have two anode rods. If there are two anode rods, that is because one is attached to a hex head at the top and the other is a combination anode attached to the hot water outlet. Some residential heaters have two hex headed anode rods and no combination anodes though.
To find out if you have a combination anode rod, disconnect the hot water outlet at the top of the heater using a pipe wrench. Don’t forget to shut off the water first! Next poke a stiff wire down the hole where the hot water nipple was. If it stops about 3 to 6 inches directly down, then you have located the combination anode. If the wire meets nothing inside, the anode is somewhere else. The combination anode can be removed with a pipe wrench.

If you do not have a combination anode and you want to install one, then remove the hot water pipe nipple and replace it with a combination anode rod. The nipple on the anode rode will need to be longer than the thickness of the insulation on top of the heater, which is usually 2 to 6 inches.


Magnesium is used more often than the other metals for anodes. When the water in your area is not particularly hard, use of magnesium rods is probably best. Be careful with magnesium rods, however, when replacing them in an already corroded tank. The electrochemical reaction from the new magnesium anode can cause hydrogen gas to build up in the tank. This can lead to water leaks.


New water heaters rarely have a zinc rod already installed. Zinc rods are actually aluminum rods with a 1/10 portion of the rod being actual zinc. Zinc’s only purpose in an anode rod is to reduce the smell of sulfur in the water.

Consumption of Anodes

Softening hard water with salt is actually more damaging to anodes than the calcium carbonate–the cause of hard water. Salt can consume an anode up to three times faster than usual. Phosphates can have the same adverse affect on an anode. The anode should be inspected every two years or sooner if you use these water softening agents.

The anode is the reason the heater stays functional for years or even decades. Anodes corrode predictably. Most times it corrodes at the top or bottom and exposes the steel wire underneath.
Core Wire

The water heater will only be protected if the anode rod has enough metal hanging on it. The steel core wire keeps the sacrificial metal on the anode. Be sure to inspect the anode for an exposed core wire every two years at least.

When analyzing an anode rod for exposed core wire, the wire can be covered in calcium carbonate that brushes off easily. This calcium carbonate is not corroded metal from the anode rod, so do not worry about removing it.

Anode Evaluation

If the anode rod has more sacrificial metal than exposed steel rod, then it is still in good shape. However, if the entire surface becomes covered in calcium carbonate and this calcium carbonate becomes hard, this will prevent the anode from protecting the tank any longer. This is known as passivation. If the anode has passivated, it will not look so by sight alone. To test for passivation, you must bend the anode rod by hand. At the bend, observe for small amounts of flaking. The anode should be replaced if more areas of the rod are exposed wire than sacrificial metal. It should also be replaced if the top or bottom of the rod has deteriorated, exposing six or more inches of exposed wire. An anode should also be replaced if the anode is less than half of the rod’s 3/4 in. diameter size. If the anode has passivated, split through its length, or has become heavily pitted, it could also be time for replacement. When all the sacrificial metal has worn away, then the steel rod will begin to wear away. After the steel rod wears away, the only thing left will be the hex head or the hot water outlet nipple if it is a combination anode. At this point, the tank will begin to corrode. If the anode is found in the above stated conditions, damage to the tank may have already occurred.

Hidden Hex Head On Newer Models

Hex heads are threaded watertight plugs about 3/4 inches in diameter. They are attached to anode rods at the top of water heaters. Some are easily seen from the top of the water heater. Other times it will be under fiberglass or under a piece of plastic. To locate the hex head, drill a shallow 1/4 inch hole through the plastic top of the water heater. Do not drill deep into the tank itself. Use a long flat-head screwdriver to probe underneath the top of the water heater to find the hex head. On gas heaters, the hex head will be the same distance from the flue as the hot and cold lines are. On electrics, the anode will be off center so as not to drop on the heating elements. A few holes may need to be dug in order to locate the hex head. Once the hex head is found, it should be permanently exposed. Use a hole saw capable of cutting plastic or metal to carve a hole big enough to allow future access to the hex head. Use two people at this point to unscrew the hex head–one to steady the tank, the other to use a breaker bar and a socket that fits the head. Anywhere from 3/4 inch to 1-1/16 inch.

In the future, when buying a new water heater, purchase only those with already exposed hex heads.

Hidden Hex Head On Older Models

To find the hex head on older water heaters, simply unscrew the screws holding the top in place, mark the placement of the top and the water heater with a marker, then remove the top to find the hex head. Alas, many heaters found in today’s buildings have foamed-in tops and can’t be removed. Again, if the hex head is not exposed at the time of purchase, don’t purchase that particular tank. Look for a tank with an already exposed hex head.

Anode Inspection

Anodes should be inspected at least every two years where softened water is used but at least every four years under normal water conditions. On occasion, the location of the anode is actually written on the water heater instructions.

Anode Installation

To remove the old rod, pull it as far out as possible, bend it, then pull it the rest of the way out. To install the new one, bend the rod directly in the middle, insert it half way, straighten it against the opening, and install it the rest of the way. Screw in the anode rod at this time. If you are unable to screw it into place because it is too bent, pull it partially out and use the opening to straighten it further. If there is not sufficient ceiling room to install the new anode rod, consider a link-anode. These anodes have many small links hooked together and look similar to links of sausages. You can also try zinc anodes because they bend far easier than magnesium ones. Another way to install an anode is to drain the water heater and tip it over enough to allow easy access for the anode.


Anodes are typically 3 feet 8 inches. Anodes should be only a few inches shorter than the tank itself. Buy anodes that are a little too long instead of a little too short. This way you can cut the anode shorter if it is too tall.

Impressed-Current Rod

In relation to commercial water heaters, there are impressed current rods. These rods do not self-generate currents like sacrificial anodes. They derive power from an electrical power source. Many commercial heaters give the location of the impressed-current rod. They do not need to be replaced throughout their lifetime. They may need periodic cleaning. Simply wipe them off with a towel. If rust appears inside a water heater with an impressed-current rod, you should either call the manufacturer, call a plumber, or install sacrificial anodes.

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