How long does a water heater last?

Q: How long does a water heater last?

A tank water heater lasts 8 to 12 years and a tankless unit 15 to 20, on the figures both Fixr and This Old House publish most often. The same sources also publish 10 to 15 years for tanks elsewhere on their own sites. The difference is what is being measured: 8 to 12 is when units typically start failing, 10 to 15 is what a maintained unit reaches. Which one you get depends mostly on the anode rod and the water.

The published figures do not agree

Source and page	Tank	Tankless	Date
This Old House, installation cost guide	8 to 12 years	20 years	June 2026
This Old House, tankless guide	8 to 12 years	15 to 20 years	June 2026
Fixr, installation guide	8 to 12 years	15 to 20 years	January 2026
Fixr, gas water heater guide	8 to 12 years	10 to 20 years	January 2026
Fixr, electric water heater guide	8 to 12 years	15 to 20 years	January 2026
Fixr, 40-gallon guide	10 to 15 years	not stated	January 2026
Fixr, 50-gallon guide	10 to 15 years	not stated	January 2026

Both publishers contradict themselves. Fixr's cost guides say 8 to 12 years in five places and 10 to 15 years in two. This Old House says 20 years for tankless on one page and 15 to 20 on another.

We are not going to pretend there is one number. 8 to 12 years for a tank and 15 to 20 for a tankless unit is what both sources publish most often and what we use across this site.

Our reading of the discrepancy, stated as such: the 10 to 15 figures appear in the FAQ sections of the size-specific guides, right next to the advice to flush the tank annually. The 8 to 12 figures appear in the sections about when to replace. The most likely explanation is that 8 to 12 describes typical units in typical service and 10 to 15 describes maintained units. Neither source says this. If you want one rule: plan financially for 10 years, and be pleasantly surprised by 15.

What the warranty tells you

Fixr puts standard tank warranties at 6 to 10 years. That is the manufacturer's own bet on the tank, and it sits below even the low end of the lifespan figures.

A 9- or 12-year warranty version of the same tank usually differs in one respect: a second anode rod, or a heavier one. That is not a marketing detail, it is the mechanism. Which leads to the part that actually determines the answer.

What actually determines the lifespan

The anode rod. A tank water heater is a steel tank with a glass lining and a sacrificial metal rod inside it. The rod corrodes so the steel does not. This Old House's plumbing expert Richard Trethewey puts it plainly: magnesium is the less noble metal, "so now this becomes the place the water wants to attack and not the steel." When the rod is gone, the tank starts corroding, and a corroded tank is the end of the appliance.

This Old House says to inspect the rod every three to five years and replace it when more than 6 inches of the core wire is visible or the rod is under half an inch thick. A replacement costs $125 to $300 fitted (Fixr, August 2025) against $900 to $3,000 for a new heater. See anode rod replacement cost.

Sediment. Both sources recommend flushing the tank annually, and Fixr says twice a year in hard water areas. Sediment on the bottom of a gas tank insulates the water from the burner, which makes the unit work harder and stresses the tank. Fixr lists rumbling noises from sediment as a sign of internal damage.

Water hardness. Fixr names hard water as the reason to double the flush frequency, and This Old House says to check the anode rod annually in hard water areas rather than every three to five years. Hard water is the single factor most likely to put a unit at the bottom of the range.

For tankless units, descaling. Fixr notes that a tankless unit that is not serviced regularly "cannot work as efficiently or last nearly as long", and specifically flags hard water and calcium build-up. This Old House prices annual descaling at $100 to $500. The 15 to 20 year figure assumes this is being done.

Why tankless units last longer

There is no tank to corrode. This Old House's cost comparison makes the consequence concrete: a tankless unit costs $1,200 to $3,500 installed against $1,200 to $2,300 for a tank, and lasts roughly twice as long. Over a 20-year horizon you buy one tankless unit or two tanks.

Fixr adds a caveat worth knowing: tankless units have been around for nearly 100 years but only became common in the last few decades, so field data on units reaching 20 years is thinner than for tanks.

How to find out how old yours is

The serial number on the data plate encodes the manufacturing date, and the encoding differs by brand. Our water heater age decoder reads it. Knowing the age turns every other decision on this site into arithmetic: whether to repair or replace, whether a repair quote is worth accepting, and whether to plan a replacement before the unit fails.

Sources

Price figures are national US ranges from the sources above as of the date shown. Your local price depends on labor rates, permits and site conditions. Read how we get our numbers.