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Water heater anode rod or sacrificial anode is an important component part in water heating and has only one purpose; to protect the metal tank from corrosion.
Most hot water heaters are equipped with one or more anode rods and are made of different materials. Anode service depends on the water conductivity as the rod deteriorates over time. This is why it is necessary to maintain it, to keep the tank in operating condition. Depleted anode rod does not affect the water taste or color and the regular inspection and replacement can extend the life of the heater.
Under normal conditions, water heater anode rod will be consumed and completely gone in four to five years (depending on water chemistry and element quality) and the metal tank will start to corrode.
Based on the number and quality of the anodes, heaters have different warranties. For example, the medium quality appliances come with the most common warranty of six years. Models that are equipped with two rods or have one large or heavy duty one are better, as they allow manufacturers to provide a longer warranty (12-years is the longest I have seen).
Tank-type water heaters, even RV type (like Atwood or Suburban) can be equipped with the Aluminum, Magnesium or Zinc water heater anode rod, but not the tankless as this type does not have a storage tank.
Depending on the water hardness, chemical structure, and hot water usage they react differently and protect the heater more or less. The inside of the anode is made of the steel wire core (stainless steel on better quality rods), which does not exist on the types of the lower quality.
The tank is typically constructed of steel and since it carries water, it has to be protected against the aggressive and acidic water nature. There are two ways how to defend the tank from corrosion: with the installation of the anode rods and built-in tank lining.
Inner tank surface is factory-covered with the glass or porcelain lining, but complete coverage is sometimes neglected due to manufacturing imperfection or damages (cracks) as the result of handling and transportation.
Potable water contains elements like oxygen, calcium, and magnesium, are making water conductive or electrolytic, allowing the electricity to flow through the water - 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 the anode and cathode and two metal surfaces, 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 the tank material is anodic than the rapid failure might occur.
As the heater tank is a cathode and in order to slow down the corrosion, manufacturers are adding another metal element, the 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 into the water. During such process, the anode rod starts depleting, sacrifices itself to protect the tank and extend its life.
This is the reason why it is called sacrificial rod or sacrificial anode.
So how long does an anode rod last?
The life expectancy of this protective element depends on several factors (water quality, material, usage, maintenance...) and it could be from 5 to over 10 years but, again, depends on maintenance and proper installation.
Two of the main problems connected to the anode rod function are smelly water or hydrogen sulfide odor and tank corrosion.
Smelly water, known as the rotten egg odor is often found in water wells, where the anaerobic bacteria is the main cause. In order to fix this problem, some plumbers recommend the anode removal, but this leads to the second problem - unprotected metal tank and corrosion.
Note: Created hydrogen gas might form high concentration which is explosive. Special care should be taken there and that is why professional anode replacement and installation is recommended.
One of the simplest and most effective ways to remove the bad odor from the tank is flushing.
Some users also mentioned in their reviews an issue when the anode is too long. As it is recommended to have an anode that is only a few inches shorter than the heater, it is not a problem to cut it down using the hacksaw.
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 will not last very long, usually a couple of years. Magnesium anodes are used as they corrode at the faster rate than the iron used for inner water storage tanks.
For extremely hard water and where conductivity is high, an aluminum-zinc anode rod might be a solution.
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 crackling, popping and gurgling noise.
If you experience rotten egg odor coming out of 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 option when replacing already depleted or dissolved 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 coming from water.
If using chlorination procedure to eliminate various bacteria that are causing the odor, remove the rod and bring it back when done.
If the length is a problem, 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 - bendable (instead one solid piece), which is great if the unit is installed in tight spaces, or there is a limited overhead clearance.
Water heater, such as AO Smith Effex is equipped with the non-sacrificial powered anode, which is a better solution than the above mentioned, as it can last a lifetime and provide 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 has a smelly odor from the heater.
Some manufacturers like Rheem water heaters Co. are producing models (Marathon) without water heater anode rod. In this case, a metal tank is replaced with plastic one.
The lifespan of the sacrificial anode rod depends on the quality of the water, usage, material, and quality. The element can last about five years, often longer, but the 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 into 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.
The hex head nut can be visible (exposed) or hidden. If it is hidden it is usually under the plastic cover on the top.
You can use the ratchet wrench with the 1 1/16' deep socket to unscrew the nut.
If the anode rod is stuck and it won't come out, you can loosen it by using the air driven impact wrench, breaker bar, even the blowtorch, and heat, but be cautious not to damage the rod and threads.
Do not use WD-40 or any other type of the penetrating oil as it might get inside the tank and contaminate water.
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 the diameter is less than half the original size. Do not wait until the rod is fully depleted.
Use these steps to replace or remove the water heater anode rod:
Be sure to use Teflon tape on the fitting threads, so it can seal tightly.
Once the anode has been replaced, open the cold water supply to the water heater to fill the tank. Check the connections for leaking. If everything is OK, turn the power back on, including the gas valve.
If only checking the part, be sure to clean the calcium-carbonate build-up.
According to some experts, an anode is one of the most important elements in water heating system - found only in tank-type, but not in tankless.
You can buy an anode cheap but keep in mind that it has an important role in the lifespan of the heater and performance. Yes, the quality and professional installation are important, but regular maintenance and service also contribute in how long they will protect... and this is why it is important to contact a professional plumber.
Note: Removal of the sacrificial anode, for any reason, will void the warranty and affect the tank longevity.