A water heater is the appliance most likely to fail catastrophically, in the least convenient place, with the most water damage. It is also the one whose age almost nobody knows.
Typical lifespan
| Type | Expected life |
|---|---|
| Standard tank, gas | 8–12 years |
| Standard tank, electric | 10–15 years |
| Tankless | 15–20+ years |
| Heat pump / hybrid | 10–15 years |
Water quality moves these numbers more than anything else. Hard water can cut years off a tank. So can a heater that was never flushed, or one running at an unnecessarily high temperature.
How to find the age of yours
There is no install-date sticker, but the serial number encodes the manufacture date. Format varies by brand; most encode the year and week or month in the first four characters. Search for your brand’s serial decoder and you will find it.
Photograph the model plate while you are down there. You will want the model number when something fails, and the plate is usually in an awkward spot behind the tank.
Signs it is on the way out
Rusty or discolored hot water. If it is only on the hot side, the tank lining is failing. Not repairable.
Popping, rumbling, or knocking. Sediment has hardened on the bottom and water is boiling under it. This accelerates failure and wastes energy.
Moisture or rust around the base. Any weeping at the tank seam is terminal. Small leaks at fittings can often be tightened; leaks from the tank body cannot.
Not enough hot water anymore. Sediment displaces capacity. A tank that used to cover two showers and now covers one is telling you something.
It is past the expected life and you are on vacation next week. Age alone is a legitimate reason to replace on your schedule instead of its schedule.
Maintenance that actually extends life
Flush it annually. Connect a hose to the drain valve, shut off the cold supply and the power or gas, drain the tank, then refill. Thirty to forty-five minutes. If you have never done it and the tank is old, be aware that a long-unused drain valve sometimes fails to reseal, which is why this is better started as a habit early.
Check the anode rod every three to five years. It is a sacrificial rod that corrodes so the tank does not. Replacing a $30 rod at year five can add years to the tank. Most people have never heard of it.
Test the T&P relief valve annually. Lift the lever, let it discharge briefly, release. If it does not reseal or does not discharge, replace it. It is a safety device.
Set the temperature to 120°F. Hotter accelerates corrosion and scale, wastes energy, and creates a scald risk.
Add a drip pan and a leak sensor. A $25 water sensor next to the tank is the cheapest insurance in the house. Some policies discount for automatic shutoff valves.
Replacement cost
| Scenario | Typical cost |
|---|---|
| Like-for-like tank, gas | $1,200–$2,200 |
| Like-for-like tank, electric | $1,000–$1,900 |
| Tank to tankless conversion | $3,000–$6,000 |
| Heat pump / hybrid | $2,000–$4,000 |
| DIY tank swap (materials only) | $550–$1,400 |
Prices include haul-away and a basic permit in most markets. Code upgrades such as an expansion tank, new venting, a pan and drain line, or seismic strapping commonly add a few hundred dollars and are not optional.
DIY is feasible for an experienced homeowner on an electric tank in an easy location. Gas involves combustion venting, which is where mistakes become dangerous. Many jurisdictions require a permit either way.
Record the install date
The single most useful thing you can do is write down when it went in, what model, who installed it, what it cost, and when the warranty ends. That one entry answers every future question about this appliance, tells you when to start budgeting, and gives your insurer or buyer a documented history.
It is also how you find out that the tank that just failed was still under a six-year parts warranty.