Visit our Popular Forums

Piggy Bank · 02-05-2016, 06:20 PM

So my friend with an SOB keeps insisting that I need to change out the anode on my water heater so it won't go out at an inconvenient time.
I pulled out the owners manual on my water heater and there is no mention about this. Just talk of flushing out sediment.

So is this something that needs to be done? If so what's the story?

Thanks in advance

Drathaar · 02-05-2016, 06:37 PM

My 2¢ worth... First, check to ensure there is one. Some water heaters don't. Second, flush the tank with a tank wand, if you don't see a lot of junk coming out, it's probably ok. If there is one, pull it and check it if you're concerned.

AnnArborBob · 02-05-2016, 06:45 PM

Our HW tank does not have an anode. Since we have similar aged units, I suspect your HW tank does not have an anode. Assuming that's the case, a periodic draining and flush as suggested above should be fine. If you travel extensively in areas known for hard water (i.e., the desert SW) you might want to do this a few times a year (we are basically full timers.) If you are a weekend warrior, once a year is probably fine.

Piggy Bank · 02-05-2016, 07:15 PM

Thanks!

idroba · 02-05-2016, 08:27 PM

Atwood water heaters used in Airstream trailers do not have an anode, and Atwood specifically recommends against using one. Their tanks are aluminum. Suburban water heaters use glass lined tanks and do use an anode and recommend their replacement periodically.

rmkrum · 02-05-2016, 10:24 PM

Or you could bite the bullet and consider a tankless water heater where all the wetted parts are copper. Stand by for a large hit in the vicinity of the wallet. We like ours...

Sent from my pocket Internet using Airstream Forums

Piggy Bank · 02-06-2016, 06:01 AM

rmkrum, nice idea.

Our philosophy is to use up before upgrade. So we are not planning to replace anything currently working, but will consider upgrades for anything that gets replaced down the line.

(except maybe lights to LED to save heat/energy)

TomKirk · 02-06-2016, 10:44 AM

As a matter of routine maintenance, I flush my Atwood water heater (6 gal) twice each year.

I also have two anodes: "One to wash; one to wear." Anodes are rotated with each flush. Anode hasta be removed anyway in order to do the flush.

Once the old anode dries out, I "dust it off" with the wire when on my bench grinder. That way, it's ready for the next rotation.

BTW - I'm a live-aboard.

Tom

JCWDCW · 02-07-2016, 10:21 AM

Ditto idroba's comment. Anodes are for protecting steel in the glass lined tanks. Not needed on aluminum. Check the owners manual

JCW

1970 Safari · 02-07-2016, 10:26 AM

Be aware that there is maintenance required on tankless water heaters also. Hard water deposits collect more quickly due to the high heat in the exchanger. Most home units require "flushing" with an "acidic" medium (vinegar water) and a pump system to remove the scale.

Units that can be vented through PVC pipe are now requiring a "drip tank" filled with marble or some such material to catch the highly corrosive condensate that collects on the inside of the flue.

Might not be totally related to mobil units but you might want to check the manufacturers recommendations before purchasing a tankless system, especially when full timing.

Rob

TomKirk · 02-07-2016, 06:23 PM

It's not what it says in the owner's manual that matters, it's the alignment of elements in periodic table.

As predicted in the periodic table, magnesium (the sacrificial anode) corrodes at a faster rate than aluminum; where water chemistry, heat, pressure, and pH are all contributing factors of corrosion.

And if the aluminum tank is the anode as Atwood claims (in their manual), it'll be the aluminum that undergoes corrosion at a far greater rate than an aluminum tank with an anode installed.

In a different example, auto makers now recommend less frequent oil change then they did years ago. 90 days or 3,000 miles has become 4,500 miles or more (with the advent of blended and synthetic oil). At the same time, they also significantly reduced the size of oil filters. In a further example, 2000 Chevy Cavaliers boasted maintenance-free automatic transmissions. Their incentive?? The big auto makers are in business to sell cars. And similarly, Atwood is in business to sell water heaters. Right or wrong, Atwood's stance is not only a selling point, but it's corporate policy. Employees hafta wholeheartedly agree with it, or else!!

If nothing else, an anode is cheap insurance. But the real test is to examine the corrosion of your anode after six months. After it's dried out, "dust it off" with a wire wheel on your bench grinder. That's when corrosion of the anode really becomes apparent.

Tom

JCWDCW · 02-08-2016, 07:39 AM

As a Chem Eng so I'm familiar with the periodic table; Galvanic corrosion or protection doesn't require much voltage differential between elements (0.4 volts for zinc against steel). Aluminum tanks on RV's have been one of the standards for quite some time. "Normal" water has little or no effect on aluminum but some High Calcium or silicate waters may be just low enough in pH to pit the aluminum. Agreed that the nearly .75 V differential between Aluminum and Magnesium is sufficient to protect Aluminum, but against what. Just sayin'....
JCW

Siegmann · 02-08-2016, 09:27 AM

Quote:

Originally Posted by JCWDCW

Agreed that the nearly .75 V differential between Aluminum and Magnesium is sufficient to protect Aluminum, but against what. Just sayin'....
JCW

If I read this right, then you confirm that a magnesium anode would protect an aluminum tank against corrosion, if there were a corrosion threat, but you're not sure there is such a threat?

JCWDCW · 02-09-2016, 08:21 AM

Yes. But I question whether there is even a threat.
As far as galvanic action, Magnesium vs Aluminum will probably dissolve faster than Zinc vs Steel given the fairly large voltage difference. Hopefully the magnesium anode is mounted in a bronze fitting; otherwise the corrosion at magnesium threads will quickly lead to leaks.

I'm kind of amused by the Atwood statement that the Aluminum is the anode. I wonder what they really meant to say? I would think the aluminum tank is isolated from the steel frame in the trailer (at least in AS and most others have wood framing), so it will not even be subject to galvanic corrosion. (Caveat is whether the 110V electric element requires the tank to be grounded to the steel frame. I don't have any experience with that option). Most trailer water pipe is plastic and the tank is mounted on the trailer side wall and sitting on the wood floor.

Aluminum forms an oxide layer that protects it from corrosion unless there is a corrosive environment that dissolves the oxide. That's probably why we are not seeing failed aluminum tanks.

I do concede that the magnesium will provide protection...just not sure it is needed. based on the longevity of my 20 -25 year old aluminum hot-water tanks in my AS trailers.

JCW

Siegmann · 02-09-2016, 10:46 AM

Maybe you have a very benign water chemistry where you are or travel? Or the heater gets limited use?

I posted this on a related thread, so you may have already read it:

I've always chalked up variable tank life to differing amounts of use, and water chemistry. Now I am wondering.

I've had three tanks with pinhole leaks over 17 years of full-timing. Not one leaked from the flue. Atwood states:

"The aluminum tank is the anode and the metals in the water serve as the cathode. Consequently, the aluminum gradually sacrifices itself and aluminum particles are carried away with the water flow. A white scaly material (aluminum oxide) often is formed around the points where the heaviest action is taking place and heat accelerates the process."

It makes sense that heat would accelerate this reaction. The flue should be the hottest portion of the assembly. Most reports are of pinhole leaks in the tank body, not the flue.

Atwood states:

"The interior of the tank consists of a 15% thickness of type 7072 aluminum (pure aluminum and zinc) that is fused to the core during the rolling process."

Now I do not know what they mean by the "rolling process". Is is creating a laminated flat stock, or the forming of the tank body? If it is the latter, are they pouring the molten alloy into the tank to yield a bonded coating? If we speculate (a dangerous thing to do) that this is the case, could their protective alloy coating be thinner in some places, and on some tanks? Could this be why some tanks last 30 years+, and others only 3 years?

I had a pinhole leak, that I presumed meant the tank was toast, and soon to fail in other locations. I fixed it with epoxy, and the tank lasted another 6 years of full-time use. Go figure.

Jammer · 02-09-2016, 11:01 AM

Quote:

Originally Posted by Piggy Bank

So my friend with an SOB keeps insisting that I need to change out the anode on my water heater so it won't go out at an inconvenient time.
I pulled out the owners manual on my water heater and there is no mention about this. Just talk of flushing out sediment.

So is this something that needs to be done? If so what's the story?

As noted upthread, recent production Airstreams all use Atwood water heaters. They have an aluminum lined tank, and are not ordinarily equipped with an anode. Recent production Airstreams use PEX (polyethylene) tubing to carry water to and from the water heater, with nonmetallic fittings.

Anodes are not a cure-all for corrosion problems. They provide protection against electrochemical corrosion when dissimilar metals are used in the water distribution system when the water has certain properties. The absence of anything more than a trivial amount of other metal (other than the water heater) in contact with the freshwater system, means there is no cathode, and electrochemical corrosion cannot take place.

There are other causes of corrosion, but an anode won't help with those. Extremely acidic water, for example, will gradually dissolve metal components in the plumbing, anode or no anode.

There are a handful of situations where the anode will make water problems worse, though these are not common.

Any water heater made of metal will eventually corrode and fail. Maintenance, at best, helps a little bit.

JCWDCW · 02-10-2016, 07:58 AM

Quote:

Originally Posted by Siegmann

Atwood states:

"The interior of the tank consists of a 15% thickness of type 7072 aluminum (pure aluminum and zinc) that is fused to the core during the rolling process."

Now I do not know what they mean by the "rolling process". Is is creating a laminated flat stock, or the forming of the tank body? If it is the latter, are they pouring the molten alloy into the tank to yield a bonded coating? If we speculate (a dangerous thing to do) that this is the case, could their protective alloy coating be thinner in some places, and on some tanks? Could this be why some tanks last 30 years+, and others only 3 years?

I had a pinhole leak, that I presumed meant the tank was toast, and soon to fail in other locations. I fixed it with epoxy, and the tank lasted another 6 years of full-time use. Go figure.

The rolled coating is actually put on as they roll the sheet of aluminum out from the ingot. Since it is a hot rolled process there is good bonding of the interior layer to the tank body. Their fabrication requires welding which means they have to get good weld penetration all the way through the tank wall; wonder what that does to the rolled coating at the seams. Was your pinhole leak on the seam?
Interesting that they use an alloy containing zinc. Presume it is to protect the main tank body, but then if zinc is dissolving over time then the coating would become porous.
Certainly your comments about time of use and corrosiveness of the water are valid. My current trailer has been extensively used over its 20 years of life. New to me, so we'll see whether the Atwood can last another 5 or 6 years.
JCW

Siegmann · 02-10-2016, 09:18 AM

Interesting.... one leaked at a seam, another leaked at the juncture of the water out fitting. You may be on to something.

markdoane · 02-10-2016, 09:49 AM

It's my opinion, and it may conflict with some of the opinions above, that the aluminum/zinc rolled-on cladding acts as the anode against the main tank stucture which is aluminum. The aluminum/zinc alloy would be a protective coating that would eventually corrode away leaving the tank unprotected after X years where X depends on the corrosivity of the local water.

Under this theory, if you use a magnesium anode in an Atwood water heater it would corrode before the aluminum/zinc alloy, and therefore extend the life of the water heater, especially if the local water is corrosive.

Depending on water quality, you could extend the life of the water heater by using a magnesium rod. Whether the extension is worth the cost of the rods and the labor rquired to periodically replace the rod depends on local water quality.

As a test, I would install a magnesium rod and check it after one year. If there was significant loss of material that would indicate to me that it was useful. You must look at the magnesium rod as protecting the aluminum/zinc cladding, rather than protecting the tank itself.

This belt, then suspenders, approach might not work for you. As I have said above, it depends a lot on your local conditions.

JCWDCW · 02-11-2016, 10:52 AM

Quote by markdoane; "As a test, I would install a magnesium rod and check it after one year. If there was significant loss of material that would indicate to me that it was useful. You must look at the magnesium rod as protecting the aluminum/zinc cladding, rather than protecting the tank itself.

This belt, then suspenders, approach might not work for you. As I have said above, it depends a lot on your local conditions." Endquote

Sensible, practical ....nothing wrong with this idea!

JCW