Anode Rod
An anode rod is a long metal rod, typically made of magnesium, aluminum, or an aluminum/zinc alloy, that threads into the top of a residential storage water heater. Its purpose is electrochemical: the rod is more reactive than the steel tank, so dissolved minerals and oxygen attack the rod first, sparing the tank lining from rust. Without a functioning anode, a glass-lined steel tank will typically perforate within 6 to 8 years; with timely replacement, the same tank can last 15 years or longer.
When replacement is needed: Most manufacturers and the U.S. Department of Energy recommend inspecting the anode every 2 to 3 years and replacing it once it is consumed below roughly 6 inches of remaining magnesium core or coated in heavy calcium scale. Homes with hard water (above 7 grains per gallon) or with a water softener exhaust the rod faster, often in 3 to 5 years. Aluminum rods are common in soft-water regions; magnesium gives stronger protection but reacts faster.
Failure symptoms:
- Rotten-egg sulfur smell in hot water (bacterial reaction with a depleted magnesium rod)
- Rusty or discolored hot water at fixtures
- Visible corrosion or weeping at the tank seams
- Popping or rumbling from sediment buildup at the tank bottom
- Hot water that runs out faster than it used to
2026 service cost: A standard anode-rod replacement runs $150 to $280, including the rod ($30 to $90), labor (about an hour), and disposal. Flexible segmented rods used in tight closet installs add roughly $50. Powered titanium anodes, which do not deplete, cost $300 to $500 installed and are useful in well-water or recirculation systems where standard rods burn out quickly.
Code reference: Anode rods are addressed indirectly in the International Residential Code (IRC) Chapter 28 and in ANSI Z21.10.1 (gas) and UL 174 (electric) water-heater standards, which require corrosion protection adequate for the tank's rated service life. Replacing the rod is a homeowner-permitted maintenance item in most jurisdictions and does not require a plumbing permit, but draining and refilling the tank should follow the manufacturer's instructions to avoid scalding and dry-fire damage on electric units.