Water heater maintenance: age, temperature, and when to replace

Find its birthday

Every tank water heater has a manufacturer's label with a serial number, and buried in those digits is the month and year it was made. The exact format varies by brand — search your brand name plus "serial number date" if you can't decode it.

Why it matters: most tank water heaters last around a decade, roughly 8 to 12 years. A typical residential tank holds 40 to 50 gallons. When a tank fails, that's 40-plus gallons of water going somewhere you don't want it. Knowing the age turns a surprise flood into a planned replacement.

The 120° setting — the full picture

120°F is the standard recommendation, and it's a good one: it balances energy use against scalding risk. According to the U.S. Consumer Product Safety Commission, most adults suffer a third-degree burn after about six seconds in 140°F water, versus about five minutes at 120°F. For most households, 120° is the right dial position.

Here's the honest nuance most advice skips: the bacteria that causes Legionnaires' disease thrives in warm water roughly between 77°F and 113°F, and the CDC's guidance for controlling it is to store hot water above 140°F. So 120° sits in a middle ground — safer against scalding, but below that storage temperature. Because of this, some plumbers recommend storing water at 140°F and installing a thermostatic mixing valve that delivers 120°F at the tap — the approach the CDC describes for preventing scalds while keeping stored water hot, at the cost of a plumber visit.

If anyone in your home is elderly or immunocompromised, don't go by an article — ask a plumber about the right setup for your household. This isn't medical advice; it's a nudge to get professional input where it counts.

Sources: U.S. CPSC, Avoiding Tap Water Scalds; CDC, Controlling Legionella in Potable Water Systems.

Replace it on your terms

A water heater doesn't send a warning. It gets older quietly, then fails loudly. The better play:

1. Learn the age from the serial number, today.

2. Check the temperature setting while you're there.

3. If it's approaching ten years, start planning. Get a quote on a calm Saturday, not at 6 a.m. with water on the garage floor.

4. Save the details — model, serial, install date, capacity — somewhere you'll find them. A photo of the label takes thirty seconds and outlasts the label itself, which corrodes in garage humidity.

A replacement you schedule is a planned expense and an afternoon. A replacement the tank schedules for you is a flood, a plumber's emergency rate, and a very bad morning.

Your home has a lot to remember. The water heater's birthday shouldn't be one of the things you have to.