How long does a water heater last?

Water heaters do not usually die suddenly — they die on a schedule you can mostly predict, and mostly influence. The headline numbers are 8–12 years for a tank and 15–20 for a tankless, but the spread within those ranges comes down to three things.

1. Water hardness

Hard water carries dissolved minerals that drop out as sediment in the bottom of a tank. That sediment insulates the burner from the water, forces longer burn cycles, and accelerates corrosion. A heater on hard water that never gets flushed can fail years early. Softened or naturally soft water is the single biggest factor pushing a tank toward the long end of its range.

2. Whether the anode rod was ever replaced

This is the part almost nobody knows about. A tank has a sacrificial anode rod inside it that corrodes instead of the tank walls — sacrificing itself so they do not. It is consumable. Once it is used up — typically 3–5 years — the tank itself starts corroding, and a corroded tank is not repairable. Replacing a $30 rod once or twice is the difference between a heater dying at 8 years and one reaching 15.

3. Whether it was ever flushed

Annual flushing clears the sediment before it can do its damage. It is the highest-value hour of maintenance a tank will ever get.

Signs it is nearing the end

• Rusty or metallic-tasting hot water — often the tank corroding from the inside.
• Rumbling or popping during heating, which is sediment boiling underneath.
• Any moisture or rust around the base of the tank. Tanks weep before they burst.
• Hot water running out noticeably faster than it used to.

Replace before it fails, not after

A water heater that fails does not politely stop working — it usually fails by leaking, sometimes 40 gallons at once, and typically into a finished space. Once a tank is past 10 years and showing any rust at the base, planned replacement is dramatically cheaper than an emergency one plus the flooring.