I have an anode rod in my suburban hot water tank. I replaced it about 6 months ago and just checked it. It looks like it was almost new with just a few whitish areas on it. Is this normal? How long does it normally last? I found a spot of rust on it at the end but that was all. Seems to me it should be more changes on it then what I found. Course I know nothing about this so I could be wrong. Jim
How long an anode rod lasts is a function of the type of water it's exposed to, so putting a number to it is impossible with any accuracy. Generally, checking it annually, perhaps when you're draining the heater for winterizing, is often enough to stay on top of it.
Anode rods are made from either magnesium or aluminum and are consumed in the electrolyte process. The white spots and some pitting on the rod are normal. The rust on the tip of the anode comes from the steel wire at the core of the anode around which the magnesium or aluminum is wrapped. As Dutch has already alluded to, how long they last depends on how much you use them, how hot the water is, the quality of the water, the quality of the tank, etc. If you have a salt water softener installed (which I doubt on an RV) the lifespan of the anode will be reduced. On my first trailer the anode lasted three season and probably longer but I sold the trailer first.
