Most homeowners are unaware that their hot water heaters are protected from the effects of internal corrosion by a simple device called a sacrificial anode rod. This rod protects any exposed surfaces of the steel tank’s inside walls from rusting prematurely. It does this by corroding away and therefore “sacrificing” itself for the sake of the tank.
The sacrificial anode rod has been employed as a longevity measure in hot water heater tanks for decades, and yet most of us have never even heard of it, know exactly what it is or what it does, or are aware that it should be routinely checked and replaced.
It is a cylindrical rod, anywhere from 9 inches to approximately 4-1/2 feet in length, depending on the size of the tank it protects. It consists of a slender magnesium or aluminum rod (for most residential applications) with a thin steel core wire and a threaded end that gets screwed into the tank through a port located at the top of the water heater.
Sacrificial Anode Rod – What Is That?
These are the two main styles of sacrificial anode rods used in most residential water heaters. The one on the left is the hex-head style rod which gets installed into its own special port. In many cases, the hex head can be seen as you look over the top of the tank, but on some models, it is covered by a plastic cap. The word "ANODE" may be molded into the cap or even embossed nearby in the top plate. In some cases, it`s located beneath an unmarked plug and then covered over with insulation.
The one on the right is a combo or outlet anode rod which gets installed into the hot water outlet. It has no independent port but rather shares the line where the hot water comes out. Both work equally well, but the combo style is a bit more work to remove and replace as it requires disconnection of the hot water line from the tank, whereas the hex head style may be removed without disturbing any of the water lines.
Most residential sacrificial anode rods are made of either magnesium or aluminum. Depending upon where you live and the type of water you have, one will generally be preferred to the other.
For treated municipal water systems, magnesium is usually the better choice. Magnesium is a more highly reactive material and for this reason, will generally provide better protection than its aluminum counterpart. In these cases where the mineral content is quite low, the high reactivity is beneficial, providing very good corrosion protection and a reasonable anode life.
However, where hard water is encountered or a softening method is employed, aluminum anodes are usually the preferred piece. In these environments, the aluminum rod proves highly reactive while the magnesium rod may be too much so, and deplete at an extremely high rate. Unless you plan on changing the anode every year or two, you should probably stick with the aluminum. Another issue with magnesium anodes in these water types is the tendency for magnesium anodes to produce a "rotten egg" or sulfur smell. Aluminum or aluminum/zinc anodes may help to reduce or eliminate this problem in these systems.
Magnesium and aluminum have a very similar appearance which makes it difficult to tell them apart through a visual examination. However, the material of hex-head style rods can usually be identified by an indicator on the surface of the threaded cap. A bump in the centre indicates it is a magnesium anode rod while a smooth surface means its made of aluminum. This is generally the case, but there are exceptions! Combo rods on the other hand, have no such readily identifiable indication upon them.
There is a vast number of different rods available from various manufacturers, for the numerous models and sizes of water heaters available. They come in various lengths, various rod diameters, different cap styles and of course in different materials.
Most water heater sacrificial anode needs can be satisfied with just a handful of rods, but we still attempt to carry as many different models of anodes as we can, generally stocking only the most popular models. For those we do not have immediately available, we can usually get them from our local supplier the next day. Others we need to bring in from out of town, so they may take a week or two to arrive at our door.
Some water heaters are installed in tighter spaces that do not provide suitable clearance for proper sacrificial anode rod removal and installation. For those situations, we also carry an inventory of specially jointed rods to allow for installation into such restricted spaces.
