A water heater installed in Birmingham and the same model installed in Gulf Shores do not live the same length of life. Inland, 12–15 years is normal. Here, 8–12 is normal, and we regularly pull units at year six.
Three things are doing the damage. First, salt in the air attacks the exterior: the fittings, nipples, connectors and the jacket seams. Second, humidity keeps everything sweating, which accelerates that corrosion and rots the drain pan out from under the tank. Third, mineral content in the water leaves sediment on the tank floor, so the burner heats grit and the steel above it runs hotter than it was designed to.
The anode rod is the sacrificial part designed to absorb all of that chemically. It is also the part nobody checks. Once it is spent, the tank lining is next in line, and that is when you get the weeping shell that no repair can fix.
Two habits fix most of this: flush the tank once a year, and replace the anode rod every three to four years. That is roughly one service visit a year against a four-figure replacement several years early. It is not a close call.
