Water Heater Anode Rod

I recall reading somewhere that water heaters have sacrificial anode rods that help reduce internal corrosion. Are these rods replacable in most heaters? I now have two Richmond/Rheem 50 Gal power vent heaters and with the new design (for flamible fumes) they're getting pretty pricey - so I'd like to take reasonable steps to extend their life.

Any thoughts/suggestions?

Thanks in advance!

edbreyer

There replaceable, but to get them out is another story, they can be a bear to almost impossible to remove.