Sacrificial Magnesium pole for hot water heater

The anode is zinc, and is actually referred to as "sacrificial zinc" in this application. It is required on SOME heaters, but not on an Atwood. This application is very common on boats that sit in salt water. There is a form of electrolysis that attacks metal surfaces due to a difference in grounds. The zinc is put in place as a sacrificial element so that the electrolytic process attacks the zinc and not the more important pieces of metal like a propeller, or propeller shaft, or engine components. Boats will have several large pieces of zinc attached to the boat in various places.
The same concept applies to motorhomes and campers that are plugged into "shore" power, and may have a difference in grounds.

Back to the question...Atwood does not require a zinc anode, and further, if someone installs one, like they did in MY Atwood, it tends to cause problems. Mine got fused to the internal threads of the heater, and was all but impossible to remove.

Jim

Atwood WH's are aluminum and need no anode. Suburban units are made like the WH in your house and are steel covered in a layer of glass. The latter requires an anode for long life.

Atwood heaters are plastic (coated?). Suburban heaters are steel and do need sacrificial anodes. On mine the drain plug includes a sacrificial zinc element, and I have a replacement waiting to replace the one that's in the tank now. It dates from the original purchase in 2002 and is still only about half gone. I expect a couple more years before I need to replace it as we have very benign city water in Anacortes (one of the top five for quality nationwide) and we always leave home with a full water tank.

Most CGs in the western states have pretty good quality water. It's limestone (calcium carbonate) in the mountains where the reservoirs are that cause hard water problems. Our mountains are all granite or volcanic in origin.

It's actually a zink anode

Atwood does NOT recommend an anode rod. Use the plastic plug, and replace it every few years because they get weak from removal and eventually break off. Not hard to remove broken bits, but it is a pain. Plugs are cheap.

Atwood water heaters do not need/require an anode rod.
Suburban water heaters do require an anode rod to prevent tank corrosion.