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Water heater anode rods or sacrificial anodes are essential components in water heating with one role only - 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 water conductivity as the rod deteriorates over time. This is why it is necessary to maintain it, to keep the tank in operating condition. A depleted anode rod does not affect the water taste or color, and regular inspection and replacement can extend the life of the heater.
Under normal conditions, the 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, 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 ones 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 is not the case with lower-quality types.
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 to defend the tank from corrosion: installing 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 oxygen, calcium, and magnesium, making water conductive or electrolytic, allowing the electricity to flow through the water - from one metal (anode) to another (cathode). By changing the water structure or material (metal in this case), the amount of electricity can be controlled.
A low resistance electrical circuit is created between the anode and cathode and two metal surfaces, where water acts as a medium, providing cathodic protection to the inside surface of the tank. This protective current keeps metallic ions at the cathodic surface (metal tank) from corroding.
If the tank material is anodic, then rapid failure might occur.
As the heater tank is a cathode and slows down the corrosion, manufacturers would add 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 a process, the anode rod starts depleting, sacrifices itself to protect the tank, and extends its life.
This is why it is called a 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 issues 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 anaerobic bacteria are the leading cause. Some plumbers recommend removing an anode to fix this problem, but this leads to the second problem - unprotected metal tank and corrosion. Here is some good info on how to deal with the rotten egg odor.
Note: Created hydrogen gas might form a high concentration which is explosive. You should be very cautious 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 by flushing the tank.
Standard water heaters are equipped with magnesium anode rods (identifiable by weld bead on the plug), and they work the best where water is not hard but is soft. If the water is hard, the magnesium anode rod will not last very long, usually a couple of years. Magnesium anodes are used as they corrode faster 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 an area where the water supply has a high PH (8+), water will react with the aluminum anode rod and form excessive amounts of aluminum hydroxide. A gel-like substance will then reside on the rod and bottom of the tank, making the crackling, popping and gurgling noise.
If you experience a rotten egg odor coming out of the hot water tap, which is the most common complaint associated with the anode, you can install a zinc anode rod. This might be a good option when replacing an 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 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 since it provides more flexibility. The rod is divided into several smaller sections (links), which makes the whole rod bendable (instead of one solid piece), which is great if the unit is installed in tight spaces or has limited overhead clearance.
Water heater, such as AO Smith Effex is equipped with a non-sacrificial powered anode, which is a better solution than the above mentioned, as it can last a lifetime and provide higher 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 are producing models such as Marathon without a water heater anode rod. In this case, a metal tank is replaced with a 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 problems as it is exceedingly corrosive, and 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 a warranty of 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.
The best time to replace a water heater anode rod 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 that they 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.
If the anode rod is stuck and won't come out, don't worry. There are several tools you can use to remove it. You can loosen the threads of the rod by using the air-driven impact hammer and wrench, breaker bar, even the blowtorch, and heat, but be cautious not to damage the rod and threads.
To remove the seized anode rod, do not use the rust dissolver such as WD-40, muriatic acid, or any other type of penetrating oils, as it might get inside the tank and contaminate water.
Tip 1: First, try to tighten the anode, just a hair, and then apply all your force but in the opposite direction (counterclockwise). This will break the corrosion on the threads. Some plumbers reported that it worked.
Tip 2: You might also have to secure the tank using a ratchet strap and wedge block as an anchor. This will prevent the heater from spinning counterclockwise while applying the force in the same direction. The idea is to apply all the torque into the rod threads, prevent the heater from moving, and at the same time protect the wall from damages.
Note: If the water heater is over 15 years old, you might want to consider replacing it because an anode might be corroded (so as other elements). Rust on the threads will make the rod challenging to remove; rust flakes can also penetrate the tank and contaminate water, or even worse, corrosion can develop leaks.
If you are trying to replace an old anode rod, but you don't have much space above the water heater to remove it freely, you can either bend or cut the anode. Once you cut it, make sure that the bottom end doesn't fall back into the tank.
If you are installing a new solid rod, make sure to use one of the same lengths. If you have purchased a longer one, cut it to the length of the previous (original) one. It is recommended to cut it to the length so there is a clearance of a few inches from the bottom of the heater.
Instead of buying a long anode and cut it to the correct size, a better idea is to get and install a flexible anode.
Does the length matter?
Of course, it does because longer it is more it can sacrifice and last.
According to some experts, an anode is one of the most important elements in the 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 a vital role in the lifespan of the heater and performance. Yes, the quality and professional installation are essential, but regular maintenance and service also contribute to how long they will protect - and this is why it is necessary to contact a licensed plumber.
Note: Removal of the sacrificial anode, for any reason, will void the warranty and affect the tank's longevity.