Water heater anode rod: when to check it, which one to install, and how to quote it

Every glass-lined steel water heater has a part that is designed to be eaten away: the anode rod. A. O. Smith calls it "the water heater's first line of defense" against tank corrosion and leaks. When it's gone, the water starts on the tank itself.

For a plumber, the anode is three things: a quick check that tells the customer something useful, a small repair that can add years to a tank, and the fix for the "my hot water smells like rotten eggs" call. This guide covers what the manufacturers and DOE research actually say about each, and how to price the work.

What the anode rod does

A glass (porcelain enamel) lining protects most of a tank, but no lining is perfect. A 2013 report by Pacific Northwest National Laboratory for the U.S. Department of Energy puts it plainly: because the glass lining is inherently imperfect, almost all manufacturers also include an anode rod.

The rod is made of a metal that corrodes more readily than steel, usually magnesium, aluminum or zinc, according to A. O. Smith. Bradford White describes it as being consumed as it gives up its electrons to protect the carbon steel tank. Rheem's manuals say the rod "is slowly consumed, thereby eliminating or minimizing corrosion of the glass lined tank." Once it's used up, nothing stands between the water and the steel at the flaws in the lining.

How often to check it

The manufacturers don't agree on one interval, so use the manual of the heater in front of you. Here is what we found:

A. O. Smith's light commercial electric manual goes further: annual inspection and replacement of the anode "is required," and it calls a rod depleted when most of it is under 3/8 inch thick or about a third or more of its length shows the support wire.

Water softeners use up anodes faster

This is the line to remember on any house with a softener. A. O. Smith's technical bulletin says customers using water softeners "should expect more rapid anode consumption," and its manuals repeat it. Bradford White asks for more frequent inspection with softened or phosphate-treated water and suggests targeting a hardness of 10 to 12 grains per gallon, because overly softened water increases conductivity. A softener on the system is a good reason to check the anode at every visit.

Magnesium, aluminum or powered

Two sources disagree on aluminum with softened water, so read the manual of the heater you're working on before you swap materials. A. O. Smith has one more caution: with water at pH 8 or above, aluminum anodes can shed aluminum hydroxide "jelly beads," and its bulletin says to replace the aluminum anode with magnesium.

Some manufacturers now offer their own powered anode kits; A. O. Smith, for example, lists an optional powered anode kit for its Vertex HV gas model. Aftermarket powered anodes exist too. Corro-Protec, for one, says its titanium anode draws about 15 milliamps at 24 volts on its 40 to 89 gallon model and costs "about $2-$3 in electricity per year."

The rotten egg smell

When a customer calls about hot water that smells like rotten eggs and the cold doesn't, the anode is often part of the story. State's manual explains that it takes sulfate-reducing bacteria in the water heater plus excess hydrogen produced by the anode's corrosion protection. The PNNL report describes the chemistry: the bacteria turn sulfate into sulfide, which combines with hydrogen from the anode to form hydrogen sulfide gas. Bradford White says the magnesium anode generates enough hydrogen to create the odor when it reacts with the sulfur and bacteria.

What the manufacturers and health agencies recommend:

• Swap the anode. Rheem: switch to an aluminum anode or a powered anode. Penn State Extension: replacing magnesium with aluminum "should eliminate the rotten egg odor while maintaining corrosion protection." State points to a zinc anode, and Bradford White to its A420 anode.
• Chlorinate the tank. Bradford White's procedure: pour half a gallon to a gallon of bleach into the heater through the hot outlet, install the A420 anode, and leave it at least 3 hours, ideally a full day. State calls chlorination "the only sure treatment" for the bacteria.
• Heat. A. O. Smith and State say a 140°F setting kills the bacteria; the Minnesota Department of Health suggests 160°F for several hours. Both carry a scald risk, so use a mixing valve and tell the customer. Bradford White notes the bacteria can survive heat up to about 225°F, which is why chlorination is the surer fix.
• Don't just pull the anode. Removing it does stop the reaction, but every manufacturer we checked says running without an anode voids the tank warranty (more below). Penn State Extension warns of the same.

If the cold water smells too, look at the well or the water supply, not just the heater. That's a water treatment conversation, and a different quote.

Removing the anode voids the warranty

The manufacturers are unanimous on this:

• A. O. Smith and State: an anode rod "must be installed in the water heater at all times or the warranty is void."
• Rheem: running with the anode removed will "exclude warranty coverage."
• Bradford White: removing any anode, except for inspection or replacement, "will nullify the warranty."

A. O. Smith and State also say anode rods are a consumable item and aren't covered under warranty. We didn't find a heater manufacturer that addresses aftermarket anodes and the warranty either way; Corro-Protec, which sells one, argues that a manufacturer can't void a warranty just because you used an aftermarket part. If the customer's tank is under warranty, use the manufacturer's replacement part or check with them first.

How to replace an anode rod

These steps follow A. O. Smith's residential and light commercial manuals. Check the manual of the heater you're working on; locations and fittings vary.

1. Shut it down. Turn off the electrical disconnect on an electric heater, or the gas control on a gas heater per its manual.
2. Cool and depressurize. Run hot water until it's cool, turn off the cold water supply valve, and open a hot water faucet to relieve the pressure.
3. Drain a little. A. O. Smith's commercial manual says to drain about 5 gallons.
4. Find the anode. It's either under a hex head on top of the tank or built into the hot water outlet nipple (a combination anode). Some tanks have both. On some electric models, you cut away foam insulation to reach it.
5. Remove it. A. O. Smith specifies a 1-1/16 inch socket with an extension.
6. Inspect and replace. Compare against the replacement rules above. Rods are typically half to three quarters of an inch in diameter and 30 to 40 inches long, says the Minnesota Department of Health, so check the ceiling height before you pull one; segmented or flexible anodes exist for tight spaces.
7. Seal and reinstall. Thread sealant tape or pipe joint compound on the threads, per A. O. Smith.
8. Refill and check. Open the cold supply, run a hot faucet until the air is purged (A. O. Smith says about 3 minutes), check the fitting for leaks, then restore power or gas.

If you're replacing the whole heater instead, the 2001 DOE fact sheet suggests adding a second anode at installation, in the form of a combination anode and hot outlet nipple. And where you set the new heater, leave service clearance above it for the next anode change; A. O. Smith's commercial manual lists changing the anodes among the reasons for adequate service clearance.

How to quote anode work

There's no official price for an anode replacement, and labor depends on how stuck the rod is and how much room there is above the tank. Build it into your price book as fixed lines instead of guessing each time:

Two habits pay off. First, when you replace a heater, write the install date and anode type on the invoice and tell the customer when the manual says to check it. Second, add the anode check to every plumbing maintenance plan visit: it's quick, it shows the customer something real, and on a house with a softener it can be the difference between a small repair and a new heater. For the full water heater checklist, see our guide to water heater code requirements, and to put all of it into fixed prices, our guide on building a plumbing price book.

Plumbo builds the quote from your own price book, so the anode, the drain and refill, and the mixing valve come out at your prices every time, and Quote Guard checks water heater quotes for forgotten items before they go out. Plumbo is on the App Store and Google Play. Try the 60-second demo →

Questions plumbers ask

How often should a water heater anode rod be replaced?

Manufacturers say to inspect it, not replace it on a schedule: A. O. Smith and State after 6 months and then yearly, Rheem yearly, Bradford White every 2 years. Replace it when it's worn: Rheem says when more than 6 inches of core wire is exposed. Softened water wears it faster.

Does a new anode rod stop the rotten egg smell?

Often, when it's paired with chlorinating the tank. Rheem recommends an aluminum or powered anode; State calls chlorination the only sure way to kill the bacteria. If the cold water smells too, check the water supply as well.

Can you remove the anode rod?

Not without losing the warranty: A. O. Smith, State, Rheem and Bradford White all say running without an anode voids or excludes tank warranty coverage, and the tank loses its corrosion protection.

What size socket fits a water heater anode rod?

A. O. Smith's manuals specify a 1-1/16 inch socket with an extension. Check the manual of the heater you're working on.

Sources

• A. O. Smith, Hybrid electric heat pump water heater manual 100379653 (anode inspection, replacement steps, warranty, smelly water), and light service commercial electric manual 100380318, checked October 20, 2026.
• A. O. Smith, Water heater maintenance, Tank water heater safety, Technical Bulletin #14 and Technical Bulletin #44, checked October 20, 2026.
• A. O. Smith, Vertex HV spec sheet (dual anodes, powered anode kit), checked October 20, 2026.
• State Water Heaters, Residential electric use and care guide 100264219 and residential gas manual 184115-000, checked October 20, 2026.
• Rheem, Residential electric water heater manual AP21980 and water heater maintenance article, checked October 20, 2026.
• Bradford White, Water heater anode rods, Hydrogen sulfide odor and chlorinating water heaters and electric installation manual 238-44422-00, checked October 20, 2026.
• Pacific Northwest National Laboratory for the U.S. Department of Energy, Impacts of Water Quality on Residential Water Heating Equipment (PNNL-22921, 2013), checked October 20, 2026.
• U.S. Department of Energy, Water heating fact sheet (January 2001), checked October 20, 2026.
• Minnesota Department of Health, Hydrogen sulfide in well water, checked October 20, 2026.
• Penn State Extension, Hydrogen sulfide (rotten egg odor) in water wells, checked October 20, 2026.
• Corro-Protec, Powered anode rod and FAQ (manufacturer's own claims), checked October 20, 2026.