Hot water tanks, whether gas or electric, utilize something called a sacrificial anode rod. The rod (or rods, depending on the make and model of the water heater) acts to prevent the shell of the tank from corroding (rusting) by being made from a material that is susceptible to galvanic corrosion more easily than the shell. Simply put, the rod dissolves and your tank does not.
A typical anode rod by itself will last about six years. If you have two anode rods, you can expect your tank to last between 8-12 years. Some tanks will go the distance – in my inspections I have seen water heaters still functioning as old as 22 years.
Aluminum anode rods are best for places with hard water. The aluminum rod will withstand harder water than any other type. Aluminum may be a health problem, so to be safe you may not want to drink hot water and make sure to run some cold water through the faucet spout before drinking the water. Keep in mind, our sodas come in aluminum cans too.
Magnesium anode rods are the most common type of anode rod. They are used in places where water is softer. They do not last very long when you have hard water, a couple years at best. This is the main reason water heaters don’t last long after the anode rod is eaten up.
Zinc anode rods are really just aluminum anode rods with a small portion being zinc. The ratio of zinc to aluminum is 1:10. The reason zinc is added is to combat any sulfur smell coming from the water. A new water heater is never installed with a zinc anode rod already in it, but it is a good upgrade if you experience rotten egg smell coming from your hot water.
Replacing Anode Rods
Replacing the anode rod in a water heater before it fails can slow down corrosion inside the tank and significantly extend the life of the water heater, sometimes even doubling it.
Depending on water conditions, an anode can last longer than normal, but many localities treat their water, which can have significant effect on the life of your heater and the anode. Sometimes water conditioning may accelerate the rate at which the anode rod is consumed. In other words, checking the anode should be a routine maintenance task.
An Excellent DIY Video can be found here: http://www.youtube.com/watch?v=97ett_HNu4k
As with all Home Improvements, if you are not comfortable with performing the work, please contact a licensed professional in your area.
Author David Fairbairn is a certified, licensed home inspector serving Vancouver and the Lower Mainland. He has been featured in the media and has contributed to "24" Newspaper, and Global TV. He has spent years working with residential and commercial building projects, and holds a Power Engineering License in BC. Why not give him a call for your next Home Inspection? Call 604 395-2795 or email firstname.lastname@example.org today!