Aluminum and magnesium anode rods are more reactive than water heater metal. Magnesium is more reactive than aluminum. Thus aluminum is good for hard water. Magnesium is good for soft water to keep up with the many corrosive elements. But, magnesium rods do not last as long and need more frequent replacement.
Difference Between Aluminum and Magnesium Anode Rods: Overview
Both aluminum and magnesium anode rods provide the function of preventing your water heater from becoming rusted and corroded. Their specific properties help them attract the reactive elements from the water that cause corrosion, and the rod itself becomes corroded as opposed to the actual tank.
Their most distinguishing difference comes from how they function. Where aluminum rods are slower at doing their jobs; magnesium ones are a lot more reactive and, therefore, perform a lot faster to attract the corrosive elements.
Aluminum Anode Rods
Relevant Characteristics of Aluminum
Aluminum makes a wonderful material for the manufacturing of anode rods as its characteristics are perfect for its function.
Aluminum is more reactive to corrosive materials than steel (what water heater tanks are typically made from), which means anode rods made of this material will preferentially corrode once it has come into contact with corrosive elements in the water.
Aluminum also has a high reactivity to hot water, which makes it suitable for use in a water heater tank as once the water has heated, the anode rod will perform faster and more efficiently.
Design of Aluminum Anode Rods
Aluminum is extremely light and capable of bending quite easily. Its light weight means that it is easy and cost-effective to transport, and the flexibility makes it easier to manufacture (it allows for customized rods to be made to suit all shapes and sizes of water heater tanks) and to install.
Some of the anode rods are not entirely comprised of aluminum.
You can get the option of purchasing an aluminum/zinc combination rod, which has majority aluminum, a small percentage of zinc, and then an even smaller percentage of trace metals. The combination of these metals provides the benefit of reducing odors from your water tank.
Ability to Handle Hard Water
Aluminum anode rods are best suited for water that has a higher pH level and is generally quite hard.
Aluminum rods withstand harder water a lot better than rods made of other metals because they are less reactive than the other metal options for anode rods.
They find the balance between lasting longer in the hard water and still preferentially corroding fast enough that the tank is protected. However, this is only applicable when there are moderate amounts of corrosive elements.
Average Lifespan of Anode Rod
Depending on just how hard your water is and the overall quality of it, your anode rod will last you a maximum of 5 years.
If you have generally hard water and have to make use of a water softener, then your anode rod will have a shorter life span as the softener will increase the corrosion of the rod.
Too much water softening can reduce the lifespan of the rod to less than a year!
You will be able to determine when it is time to replace your anode rod when the inner tubing becomes significantly exposed.
A few holes are normal and indicative that the rod is performing well, but when a large portion of the inside cable becomes visible, you are at risk of damage to the tank of your water heater.
Cost of Aluminum Rods
Aluminum rods are often the first choice for people as they are the lowest-priced metal rods of the available options.
Aluminum is the most widespread metal on the planet, so the abundance of availability makes them super affordable.
You can find one of these rods for around $15, and they are readily available to purchase from most home-good stores and even online.
Magnesium Anode Rods
Relevant Characteristics of Magnesium
Magnesium is a suitable metal to use for the manufacturing of an anode rod as it has certain characteristics that assist in the process of sacrificial corrosion.
Magnesium is highly reactive to corrosive elements, more than steel and more than aluminum, which makes it really suitable for its function as an anode rod.
Magnesium also releases more electrons than aluminum does, which is why it works so effectively as the electrons are needed for the electrochemical process to occur to allow for the corrosion to take place on the rod and not on the water heater itself.
Design of Magnesium Anode Rods
Magnesium anode rods are generally quite light, making them convenient to transport and install.
These rods are not usually just made of one metal but are also comprised of other trace metals, although the main metal portion is magnesium.
Ability to Handle Hard Water
Unlike aluminum rods, magnesium anode rods should not be placed in water heaters that receive hard water. They will be corroded too quickly, faster than necessary to protect the tank from hard water.
Your anode rod will rapidly become covered in limescale or corroded to the point where it can no longer function efficiently, and if left unreplaced for too long, your water heater tank will start to rust.
So, why do magnesium rods even exist? The very feature that makes these rods a poor choice for hard water makes them the best choice for softened water.
Note: soft water is different to softened water. The former refers to a natural lack of hard elements in the water; the latter refers to the addition of corrosive salts to counteract the hard minerals.
Softened water contains too many corrosive materials for the aluminum anode rods to keep up. While the rod is reacting at its slower rate (compared to magnesium rods), there’s plenty of time and corrosive materials to also react with the tank.
You would have to replace the rod frequently than you would in naturally soft water, but at least your tank would still be protected.
Average Lifespan of Anode Rod
Despite its benefits, magnesium anode rods tend to last for a shorter period of time than aluminum rods under all conditions.
The difference is not too significant under normal conditions as research shows that these rods can also last up to 5 years, but it all depends on the quality of the water that runs through your water heater. It is common for one to have to replace a magnesium rod after just 12 months.
Cost of Magnesium Rods
Magnesium rods are not as cheap as aluminum rods, but they won’t necessarily break the bank either. Depending on the size of your water heater, and therefore the required size of the anode rod, you can expect to pay a minimum of $30 for a magnesium anode rod.
Table of Differences Between Aluminum and Magnesium Rods
| Aluminum Anode Rods | Magnesium Anode Rods |
| Better suited for hard water | Better suited for softened water |
| Has a longer lifespan as it takes longer to corrode | Will not last as long as an aluminum rod as corrosion occurs faster |
| More affordable than a magnesium rod | More expensive than aluminum rods |
Should I Use an Aluminium or Magnesium Anode Rod?
The choice of which anode rod you should use comes down ultimately to the type of water that flows through your house.
Aluminum anode rods are better suited for houses that suffer from hard water, whereas magnesium anode rods work best in softened water. However, if you live in an area where your water is not that hard nor that has been artificially softened, then the choice is yours.
Your decision can be made based on your budget and how long you are willing to wait before needing to replace the anode rod.
If you are struggling with smelly well water, then neither magnesium nor aluminum anode rods is going to be your best choice. Rather go for a zinc alloy rod.
Of course, you could always go with a water heater that does not need an anode rod; not all of them do.
Do Magnesium Anode Rods Provide Health Benefits?
If you look online for the pros and cons of magnesium anode rods, you will likely come across claims that the breakdown of magnesium anode rods releases magnesium into the water, which comes with health benefits.
Magnesium is a substance that is helpful in your body, but I can find no scientific research to back up the claim that anode rods have notable health benefits.
Sources
https://tanklesswaterheaterexpress.com/water-heater-anode-rod-aluminum-vs-magnesium/
https://www.nebraskyplumbing.com/everything-you-need-to-know-about-a-water-heater-anode-rod/
https://www.metalswarehouse.co.uk/lifespan-recyclability-aluminium-steel/
https://www.kloecknermetals.com/blog/what-are-the-major-properties-of-aluminum/
https://cathwell.com/aluminium-vs-zinc-anodes/
https://lahaaland.com/water-heater-anode-rod-aluminum-vs-magnesium/
https://www.doityourself.com/stry/5-types-of-water-heater-anode-rods-explained
https://www.healthline.com/nutrition/10-proven-magnesium-benefits#TOC_TITLE_HDR_2
https://www.hydro.com/en-US/aluminum/about-aluminium/aluminum-and-health/