The manufacture of conventional water heater tanks involves the use of a metal vessel that is finished with a porcelain enamel coating on the inside wall. This coating provides the primary protection of the tank’s steel wall, but it is never perfect. There are always microscopic bare metal spots present, not to mention other exposed metal areas due to chips and cracks sustained during processing and handling, and in transitions and fittings such as at the thermostat, the inlets and outlets, and even the drain in many cases. During service, further cracks and exposed metal areas develop as the porcelain lining is slowly degraded. This results in further bare metal areas subjected to attack by exposure to the tank’s own hot water - the corrosive effect it has on these metal walls needs to be minimized to ensure long water heater tank life.
Cutaway view of the inside of a failed, leaking residential gas-fired water heater. The porcelain lining is seen throughout with areas of degraded coating visible on the bottom as well as the centre exhaust stack. The white tube at the left is the dip tube providing cold water to the base of the tank, while a depleted sacrificial anode with calcium build-up is seen to the right. The hole at the back near the top is where the T&P valve is mounted, while the hole at the back about 1" above the bottom left between the dip tube and the exhaust stack is where the drain valve is installed.
NOTE: The anode should actually be installed in a port at the front of the tank but has been shown here in a water port to improve visibility.
Why Do We Need These Sacrificial Anodes?
In comes the sacrificial anode rod! It is the secondary line of defence employed by the water heater, protecting any exposed metal areas. Once assembled, the interior porcelain enamel coating can no longer be improved, or upgraded, but the sacrificial anode is cleverly designed to be removable so it can be replaced as necessary.
However, the down side is the sacrificial anode rod is consumed as it protects and it therefore, has a finite life. While doing its job to protect the tank walls, it is slowly depleted and the available amount of protective material keeps reducing until the anode is useless. Meanwhile, calcium deposits accumulate and may slow down the reaction. Any exposed metal begins to corrode at an accelerated rate and will result in rust through and a leaky vessel – There’s your leaking tank – time to replace it!
This could be delayed substantially by inspecting and replacing the anode rod regularly. Many of us normally associate regular routine preventive maintenance with other items such as our furnaces, our air conditioners and of course, our cars. Replacing your anode regularly would be somewhat akin to changing your oil in your car. You wouldn’t think of letting your car run on the same oil for its lifetime, as it would ultimately, no longer protect your engine and result in failure. The anode is similar to this in its function in your water heater. As the anode protects your tank, it eventually becomes inefficient and ineffective. For this reason, ALL MANUFACTURERS recommend replacement based on similar criteria.
As your tank gets older, it becomes more and more susceptible to corrosion and therefore, proper maintenance and the sacrificial anode become more and more important. The porcelain lining begins to degrade with time, resulting in more exposed metal surface and places a higher burden on the anode for protection. That is why we suggest for best results and cost effectiveness to flush the tank and inspect the anode every 3 years and change it out after every 6 to 9 years at the latest, depending upon your actual tank and warranty, This will maximize your water heater's protection and longevity while minimizing your overall costs in the long run.