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Is water heater corrosion a sign it's time for replacement?
Thursday, December 9, 2021
Visible corrosion, especially around the bottom or top of a water heater, usually means you will need to replace it soon. But not always. The rust that happens on the inside of the tank of your water heater is what causes it to fail, and that sometimes progresses at a different rate and for different reasons than the rust on the outside.
How fast the outside of your water heater corrodes depends primarily on the environment where it is installed. The high humidity of a garage or attic speeds up rust on both the shell and any pipe connections faster than at an indoor location. But corrosion of the tank is caused by something different: an electrolytic reaction between the water and tank. The tank has both a glass lining and a sacrificial anode for protection against corrosion. An anode literally sacrifices itself and corrodes away first to save the tank. But if the anode is not checked and replaced when used up, tank corrosion accelerates rapidly. And the tank lining provides a barrier, although eventually the corrosion overtakes it.
It is possible for a water heater in a hallway closet with a sacrificial anode that is toast to both look fine on the outside and be about to start leaking soon on the inside, and it does happen sometimes. But typically the inside and outside corrode roughly in tandem. So rust, along with that powdery white buildup of galvanic corrosion at the pipe connections, usually means replacement ahead.
If your water heater has corrosion that is spreading, and it's more than 12-years old, and in a location where leakage would damage your house—wood floors around it, for example—you might consider doing a “preemptive strike” and change it now.
Also see our article What can I do to make my water heater last longer?
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