How long does a tankless water heater last?

A tankless water heater typically lasts about 20 years. The home builders’ survey puts it at 20 years or more, and a US Department of Energy guide says up to 20, against 10 to 15 for a tank.

What the published figures say

YearsSourceWhat the figure is
20 or moreNAHB and Bank of America Home Equity, Study of Life Expectancy of Home Components (2007)Survey of manufacturers and trade groups.
Up to 20US Department of Energy, Building America measure guideline: transitioning to a tankless water heaterCompared with 10 to 15 years for tank-type heaters.

The sources measure different things, which is why they differ. A survey of first owners gives a shorter figure than an analysis that follows units until they are scrapped. All of them describe typical equipment. A given unit can fail sooner or run far longer, and age alone is not a reason to replace anything that works safely.

How old is yours?

The build date is coded into the serial number. Where to find it: How old is my water heater?

Find the age from the serial number

Look for “Serial”, “Serial No.” or “S/N” on the rating plate. It is not the model number. What you type stays in your browser.

What shortens or extends its life

  • Scale in the heat exchanger. Hard water coats the narrow passages, and the heater runs hotter to push the same heat through.
  • Skipping the periodic flush that the manufacturer specifies to remove that scale.
  • A unit that is too small for the house runs at full fire for long periods.

Signs that replacement is near

  • Error codes that return after service.
  • Water temperature that swings during a shower.
  • Lower flow of hot water than before, which points to scale.
  • A leak from the heat exchanger. On an old unit that usually means replacement.

Sizing the replacement

Sources

Other equipment

Figures last checked against their sources on October 5, 2026. Method and sources.