Before we get into the water heater anode rod aluminum vs magnesium argument it’s important to take a look at what an anode rod does in your water heater.
Water Heater Anode Rod Guide
Note: tankless water heaters do not contain an anode rod however, standard tank-style water heaters do.
An anode rod helps prevent corrosion of a water tank and its elements and is often referred to as the “sacrificial anode” by experts.
Tank style water heaters come under a lot of pressure from the acidity of the water and heat produced in the tank which both speed up the process of corrosion in a water tank. An anode rod will corrode before the other elements and components of a water heater. When it does it delivers electrons into the tank which help to prevent your water heater from rusting. This method is known as electrolysis. In simple terms when you have the two pieces of metal in water, the anode and the steel water heater, the anode will corrode instead of the water heater. This occurs because the less reactive (more noble) metal (the anode rod) corrodes more than the more reactive (less noble) metal (the steel water heater).
Common less noble than steel metals used for anode rods include: Aluminum, magnesium and zinc.
As the anode rod sacrifices itself it means that your water heater will outlive it and as such your anode rod will need replacing. Typically this means replacing the rod every 3-5 years however the speed of corrosion depends on a number of different variables which may speed up or slow down the level of corrosion on your anode rod.
Water Heater Anode Rod Aluminum vs Magnesium – Which is better?
Note: We do not compare zinc anode rods here as they are actually just aluminum rods with a small portion of zinc. A zinc anode rod however is useful for combating rotten egg smell (sulfur) that may come from the water. If you experience a rotten egg smell then an upgrade to a zinc anode rod may be a good idea.
choosing the right anode rod mainly comes down to the level of hardness in your water. For harder water an aluminum anode rod is the best choice for your heater and if you live in an area with soft water then a magnesium anode rod is your best choice. Aluminum anodes tend to be cheaper than magnesium anode rods. A magnesium rod will generally last less than an aluminum rod.
One issue with aluminium rods is that the corrosive material that is formed on the anode tends to harden and sink to the bottom of the water tank. This can potentially find its way into your taps and cause issues down the line.
Our overall decision in the water heater anode rod aluminum vs magnesium argument is that magnesium anode rods are the better choice when deciding which anode to buy for your water heater.