Quick answer
A water heater anode rod is a long metal rod, usually magnesium or aluminum, screwed into the top of a tank water heater that corrodes on purpose so the steel tank does not, which is why it is called a sacrificial anode.
It is a consumable part. A.O. Smith says to inspect it at six months, then at least yearly, and replace it when worn. Once it is gone, the tank starts to corrode.
Quick facts
The key facts about Water Heater Anode Rod, with sources:
- Job
- Corrodes in place of the tank to prevent leaks 1
- Typical size
- ½ to ¾ inch across, 30 to 40 inches long 4
- Inspect
- After 6 months, then at least yearly (one maker) 1
- Softened water
- Rod depletes faster (one maker) 1
- Socket size
- 1-1/16 inch on one maker’s heater 1
- Warranty
- Tank warranty void without an anode in place (one maker) 1
Key takeaways
- The anode rod is the tank’s rust protection; when it is used up, the tank starts to corrode.
- One major maker says check it at six months and then every year, more often with a water softener.
- A rotten-egg smell from hot water only often comes from a reaction at a magnesium anode.
- Swapping the rod type can help the smell; removing it shortens tank life and can void the warranty.
- Anode rods are not covered under at least one maker’s warranty: they are a consumable.
A rod that is meant to wear out
Inside a tank water heater, hot water sits against a steel tank lined with a thin glass coating that always has tiny flaws, and wherever water reaches bare steel through those flaws, the steel rusts. The anode rod stops that by giving corrosion an easier target.
Metals like magnesium and aluminum give up electrons more readily than steel. When the rod and the tank sit in the same water, the rod corrodes first and the tank is spared. A.O. Smith calls it a sacrificial metal rod that helps avoid corrosion and premature leaks 1.
The rod is long and thin. Minnesota’s health department describes it as ½ to ¾ inch in diameter and 30 to 40 inches long 4. It hangs from a hex head in the top of the tank, or on some heaters it is built into the hot water outlet fitting.
How the protection works
- Water in the tank conducts a small current
- Anode rod (magnesium or aluminum) gives up metal
- Steel at flaws in the glass lining is protected
- Rod shrinks over months and years
- Rod used up: tank steel corrodes, then leaks
- NewFull-thickness rod
- Partly depletedPitted, thinner, core wire starting to show
- Fully depletedMostly bare core wire; replace 1
- No protectionTank lining flaws begin to corrode
Source: [1]
The rate depends on your water. A.O. Smith says a water softener makes the rod deplete faster than normal 1. That is why there is no single replacement interval that fits every house. The only way to know is to pull the rod and look.
Magnesium, aluminum, zinc and powered anodes compared
| Type | What sources say | Use it when |
|---|---|---|
| Magnesium | The usual factory rod 42; can react with sulfate to make hydrogen sulfide 24 | Standard choice where water has no odor problem |
| Aluminum | Penn State says replacing magnesium with aluminum should end the odor and still protect the tank 2 | Rotten-egg smell from hot water only |
| Zinc (aluminum-zinc alloy) | A.O. Smith says a special zinc anode may help reduce or eliminate the odor 1 | Odor problems, per the heater maker |
| Combination (outlet) anode | Built into the hot water outlet nipple on some heaters | Heaters without a separate anode port |
| Powered anode | Uses a small electric current instead of wearing away | Ask the heater maker first; it affects the warranty |
Example: an inspection schedule for one household
A worked schedule using A.O. Smith’s guidance to inspect at six months and at least yearly after, sooner with a softener 1. The install date is illustrative.
| When | What to do | Basis |
|---|---|---|
| Heater installed, January | Note the date and the anode location | Rating plate and manual 1 |
| Month 6, July | Drain, flush and pull the anode for a first look | A.O. Smith 1 |
| Month 18 | Inspect again; replace if substantially worn | At least yearly 1 |
| With a water softener | Inspect more often than yearly | Rod depletes faster 1 |
| Hot water smells like rotten eggs | Consider an aluminum or zinc rod; do not just remove it | Penn State, A.O. Smith 21 |
The point of the schedule is to catch the rod before it is gone, because a rod is a consumable part while a corroded tank usually means a new water heater. The sizes below decide whether you can pull the rod at all in a low closet or attic.
Where to find it on your heater
Look at the top of the tank, where most heaters have a separate hex head, often hidden under a plastic cap or a patch of foam insulation.
A.O. Smith’s gas heater diagram lists the anode at the top of the tank, not visible from outside 1. On some models the rod hangs from the hot water outlet instead.
Your manual and the rating plate name the model, which tells you the rod type and length. On a plumber’s invoice, the job appears as "anode rod replacement," often paired with a tank flush. It falls under water heater repair and replacement.
Why it matters
A rod with metal left
A depleted rod
- Tank steel begins to corrode at lining flaws.
- Rust-colored hot water and eventual leaks.
- Not covered under warranty as a consumable 1.
- Seized rods can be hard to remove.
What an anode rod cannot do
A new rod cannot repair a tank that is already leaking, because once water seeps from the tank body the steel wall itself has rusted through, and the heater needs replacing.
It also does not fix sediment: hard water leaves calcium carbonate scale in the bottom of the tank, which makes popping noises and slows heat transfer, and only draining and flushing the tank removes it.
And tankless heaters have no storage tank and no anode in the same sense, so this part is a tank-heater concern.
What makes anode replacement cost more or less
We do not quote prices, because fair numbers need dated local quotes. The rod is a modest part.
What moves the cost: whether the hex head is seized; ceiling height above the heater, since a long rod needs clearance or a flexible segmented rod; the rod type (aluminum, zinc or powered); and whether a flush is done on the same visit.
The bigger comparison is a rod against a whole new heater. Our repair vs. replace tool weighs age, symptoms and condition, and the cost guide explains what drives water heater prices.
How an anode rod is inspected or replaced
A summary of the maintenance order in A.O. Smith’s Use and Care Guide 1. Check your own manual; many owners hire this out.
- Turn the heater off as the manual describes and let the hot water cool; A.O. Smith says this may take 10 minutes or longer of running hot water.
- Turn the cold water supply valve off.
- Open a hot tap and drain some water from the tank so the rod port is below the water line.
- Use the correct socket (1-1/16 inch on the A.O. Smith model) to loosen and lift the rod.
- Compare the rod with the maker’s pictures of new, partly depleted and fully depleted rods; replace if substantially worn.
- Wrap the new rod’s threads as the maker directs, install it, and tighten.
- Refill the tank completely with a hot tap open until water flows steadily, then restore power or fuel per the manual.
- Check the fitting for leaks.
Hot water, gas and electricity
Tank water can scald: CPSC says 140°F water causes third-degree burns in about six seconds 5. Let it cool first. Never heat an empty tank; refill before turning it on.
On a gas heater, follow the manual exactly and leave anything involving the gas line or venting to a licensed pro; if you smell gas, leave and call the utility or 911.
Do not raise the tank temperature to fight odor without a pro.
How to keep the anode doing its job
- Inspect the rod at six months and at least once a year after, per A.O. Smith 1.
- Check more often if you have a water softener 1.
- Flush sediment at the same visit; A.O. Smith pairs the two tasks 1.
- Keep a replacement rod of the right type and length on hand.
- Note each inspection date on the heater or in your records.
Signs the anode rod is used up
- Hot water only smells like rotten eggs 34.
- Rusty or discolored hot water while cold runs clear.
- The rod, when pulled, is mostly bare core wire 1.
- Water around the base of the tank: a possible tank leak.
- The heater is several years old and the rod has never been checked.
If water is leaking from the tank body, the rod is too late; plan for a replacement. See plumbing emergencies if it is leaking fast.
Rules, warranties and health guidance
Manufacturer warranty: A.O. Smith says an anode rod must be installed at all times or the warranty is void, and that anode rods are consumables not covered under warranty 1. Penn State Extension says removing the rod will likely void the manufacturer’s warranty 2.
Health guidance: Penn State says hydrogen sulfide has no drinking water standard and the nose detects it well before it causes health concerns 2.
Vermont’s health department says the smell usually does not mean poor water quality but recommends testing for coliform bacteria and nitrate, since the gas can rarely come from pollution 3.
Scald limits: CPSC urges setting water heaters to 120°F 5. A.O. Smith says if the thermostat is set above 120°F, thermostatic mixing valves at each point of use are particularly important 1.
Plumbing codes do not set anode rod intervals; the maker’s manual does. Checked 2026-10-12.
Anode rod vs. other water heater parts
| Part | Job | Sign of trouble |
|---|---|---|
| Anode rod | Corrodes to protect the tank 1 | Rotten-egg smell, rusty hot water |
| T&P relief valve | Opens on high temperature or pressure | Drips or discharges |
| Dip tube | Sends cold water to the tank bottom | Lukewarm water, plastic bits in aerators |
| Drain valve | Lets you flush sediment | Drips or clogs |
Anode rod myths that shorten a heater’s life
- Myth A smelly anode should simply be removed.
- Reality Penn State and A.O. Smith say removal shortens tank life or voids the warranty; swap the type instead 21.
- Myth The anode lasts as long as the heater.
- Reality It is a consumable; inspect at six months and yearly 1.
- Myth Rotten-egg hot water means the water is unsafe.
- Reality Usually not, but test for bacteria and nitrate to be sure 3.
- Myth Softened water protects the rod.
- Reality A.O. Smith says softened water depletes it faster 1.
- Myth All heaters use the same rod.
- Reality Length, thread, metal and location vary by model.
Your water decides how fast it wears
Regional water chemistry is the big variable. Sulfate-rich groundwater, common on private wells in parts of the upper Midwest, is where hot-water rotten-egg odor shows up; Minnesota’s health department and Penn State Extension both describe the anode reaction 42.
Hard-water regions often use softeners, which wear rods faster 1. Check your water hardness, and if you are on a well, test for sulfate and bacteria.
When to replace the rod and when to replace the heater
Replace the rod when the tank is dry and sound and the rod is worn. Replace the heater when the tank leaks, the heater is old and the rod has never been changed, or repairs keep stacking up. If only the hot water smells, consider an aluminum or zinc rod rather than removing it.
Next step: find your heater’s model number, look up the rod location and type, and book an inspection if it has never been checked.
Sources differ on the replacement metal
Penn State Extension recommends aluminum to end the odor 2; A.O. Smith suggests a special zinc anode 1. Vermont’s health department lists replacing or removing the magnesium anode and notes removal may shorten heater life 3. Ask your heater maker which rod keeps the warranty.
Questions about Water Heater Anode Rod
What happens if you never replace the anode rod?
Once the rod is used up, nothing is left to corrode in place of the tank, so the water starts attacking bare steel at flaws in the glass lining.
A.O. Smith describes the rod as the part that helps avoid corrosion and premature leaks, which is what you are risking: a tank that rusts through and has to be replaced. Rusty hot water can be an early sign.
Inspecting the rod on the maker’s schedule is how you catch it first.
How often should a water heater anode rod be replaced?
Replace it when it is substantially worn, which you only learn by inspecting it. A.O. Smith says inspect after the first six months and at least once a year after that. Homes with water softeners should check more often because the rod depletes faster.
How do I know if my anode rod is bad?
Pull it and look. A rod that is mostly bare core wire is used up. Other signs include rusty hot water and a rotten-egg smell from the hot tap only. A.O. Smith’s manual shows photos of new, partly depleted and fully depleted rods.
Why does my hot water smell like rotten eggs?
A magnesium anode can react with sulfate in the water to form hydrogen sulfide, and warm tanks can host sulfur bacteria. If only the hot water smells, the water heater is the likely source, according to Minnesota’s and Vermont’s health departments.
Should I remove the anode rod to stop the smell?
No. Penn State Extension says removal can increase corrosion, shorten the heater’s life and likely void the warranty. A.O. Smith says a rod must be in place at all times for the warranty. Swap the rod type instead.
Aluminum or magnesium anode rod: which is better?
Magnesium is the usual factory rod. Penn State says switching to aluminum should end a rotten-egg odor while still protecting the tank. A.O. Smith instead suggests a special zinc anode for odor. Check which types your heater maker approves.
Does a water softener affect the anode rod?
Yes. A.O. Smith says a water softener makes the anode rod deplete faster than normal, so the rod should be inspected more often and replaced when depleted.
Can I replace an anode rod myself?
Some owners do. It requires shutting the heater down per its manual, cooling and partly draining the tank, and breaking loose a tight hex head, often with a 1-1/16-inch socket. Low ceilings, seized rods and gas heaters are good reasons to call a plumber.
Do tankless water heaters have anode rods?
The sacrificial tank anode is a storage tank part. Tankless units heat water as it passes through and do not hold a tank of standing water in the same way. Check your tankless unit’s manual for its own maintenance, such as descaling.
Sources
- A.O. Smith, Residential Standard Gas Ultra Low NOx Water Heater Installation Instructions and Use and Care Guide, retrieved .
- Penn State Extension, Hydrogen Sulfide (Rotten Egg Odor) in Water Wells, retrieved .
- Vermont Department of Health, What You Need to Know About Hydrogen Sulfide in Drinking Water, retrieved .
- Minnesota Department of Health, Hydrogen Sulfide in Drinking Water fact sheet (copy hosted by Crow Wing County, MN), retrieved .
- U.S. Consumer Product Safety Commission, Avoiding Tap Water Scalds (Publication 5098), retrieved .
Expert review
Written by the HyrePlumber Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Purpose, inspection timing, softener effect, socket size, warranty terms, zinc-anode suggestion and maintenance order are from one A.O. Smith Use and Care Guide (single maker, labeled).
Magnesium-sulfate reaction, aluminum recommendation and warranty note from Penn State Extension; hot-water-only diagnosis and testing advice from Vermont Department of Health; rod dimensions from a Minnesota Department of Health fact sheet.
Scald figures from CPSC. Where sources differ on replacement metal, both are shown. Combination and powered anode rows are general description. No prices.
Suggest a correction. We fix errors and say what changed.