Anode Rod: What It Does and When to Replace It

A water heater is a steel tank holding hot water — conditions that should corrode it through in a few years. It doesn't, because of one inexpensive component doing the corroding on its behalf.

Anode rod types

Check it every 2–3 years. Replace when the rod is under about ½ inch thick or the steel core wire is exposed along its length. A rod costs a fraction of a tank — this is the highest-return maintenance item on a water heater.

How does an anode rod protect a water heater?

Put two dissimilar metals in an electrolyte — water — and the more reactive one corrodes preferentially. That's galvanic corrosion, and a water heater uses it deliberately.

The anode rod is made of a metal more reactive than steel: magnesium, aluminum, or an aluminum-zinc alloy. It corrodes first, sacrificing itself so the tank lining doesn't.

Hence "sacrificial anode". It is designed to be consumed.

When it's consumed, protection ends and the tank begins corroding. That's when tanks start leaking — and a leaking tank is not repairable.

Why this matters more than anything else you do

Water heater failure is almost always tank corrosion. Elements, thermostats, valves, and thermocouples are all replaceable parts. A corroded tank is a new water heater.

So the component that determines how long the tank lasts is the anode rod — and it costs a small fraction of a replacement.

Most people never check it, which is why tanks that could have run 20 years fail at 12.

Types

Magnesium. Most protective, most reactive, consumed fastest. Standard in many units. The type most associated with the rotten-egg smell issue.

Aluminum. Longer-lasting, slightly less protective. Better suited to hard water and to areas where magnesium is consumed rapidly.

Aluminum-zinc. The usual answer to sulfur smell. The zinc content disrupts the bacterial reaction that produces hydrogen sulfide.

Powered (impressed current). An electrically powered anode that isn't consumed at all. Higher upfront cost, no replacement needed, and it also addresses the smell issue. Worth considering where water chemistry destroys conventional anodes quickly.

How often should you check an anode rod?

Every 3–5 years is the common recommendation, with the first check earlier if your water is aggressive.

What drives consumption rate:

• Softened water consumes anodes much faster. Water softeners increase conductivity, accelerating galvanic action. If you have a softener, check more often — every 2 years is reasonable.
• High water temperature accelerates it.
• High usage — more fresh water through the tank means more dissolved oxygen.
• Well water chemistry varies widely and can be aggressive.

Replace when substantially consumed — commonly described as when the steel core wire is exposed along much of its length, or the rod has thinned severely.

How do you replace an anode rod?

The rod threads into the top of the tank, either under a cap or combined with the hot water outlet.

The process: shut off power or gas, shut off the cold supply, relieve pressure by opening a hot tap, drain a few gallons to drop the level below the rod, then unthread it.

Two practical difficulties:

It's tight. Factory-installed anodes are torqued down and then corroded in place for years. A breaker bar and a socket are usually needed, and the tank has to be braced so it doesn't rotate or shift.

Clearance. A full-length rod is nearly as long as the tank is tall. In a basement with low joists or a closet, there may not be room to withdraw it — segmented (flexible) anode rods exist for exactly this, jointed so they can be angled out.

If those obstacles put you off, it's a reasonable plumber task, and it's still far cheaper than a new water heater.

Why does my hot water smell like rotten eggs?

A common complaint: hot water smells of sulfur, cold water doesn't.

Cause: sulfate-reducing bacteria in the water react with a magnesium anode, producing hydrogen sulfide gas. It's unpleasant, not dangerous.

Fixes, in order:

1. Switch to an aluminum-zinc anode. Usually resolves it.
2. Consider a powered anode, which eliminates the reaction entirely.
3. Raise the temperature temporarily to suppress bacteria — done with care, and paired with a mixing valve if you keep it high. See water heater temperature setting.
4. Removing the anode entirely stops the smell and destroys your tank. Don't.

That last option gets suggested online. It trades a smell for a tank failure.

While you're in there

If you're already draining the tank to access the anode, flush the sediment out at the same time — it's the other maintenance item that affects capacity and efficiency. See how to flush a water heater.

Warranty note

Longer-warranty water heaters are frequently the same tank with a larger or second anode rod. That's much of what you're paying for in a 12-year model versus a 6-year one.

Which means: a 6-year model with a replaced anode can outlast a neglected 12-year model. The maintenance matters more than the badge.

Where to go next

• How long does a water heater last
• How to flush a water heater
• Water heater installation cost
• Run the numbers: electricity cost calculator

More in our heating and cooling guides.