The traditional tank water heater is on a clock. Most last 8-12 years. Once a tank starts to fail, the failure mode is almost always the same — slow corrosion that eventually breaches the tank.
Warning signs
Discolored hot water
Brown, rust-colored, or sediment-filled hot water. Strongest signal the tank is near end-of-life.
Rumbling or popping
Sediment buildup at the tank bottom. Steam pushing through it makes distinctive sounds.
Moisture around the base
Consistent moisture, dampness on the floor, or visible streaks down the tank's exterior.
Lukewarm or inconsistent hot water
Heating element or burner failing, or dip tube cracked.
Age
Most important factor. Past 8 years, every warning sign deserves more weight. Past 12 years, replacement is usually better than repair.
Replacement options
Traditional tank (gas or electric)
Like-for-like replacement. Cheapest upfront. 8-12 year lifespan.
Cons: standby heat loss, finite hot water, eventual catastrophic failure.
Tankless (on-demand)
Heats water as it flows. No tank. 15-20 year lifespan. Unlimited hot water, more efficient, no catastrophic failure. Higher upfront cost, may require gas or electrical upgrades.
Heat pump water heater
Uses electricity to move heat from surrounding air into water. Highly efficient. Eligible for federal tax credits and many state rebates. Needs adequate ambient air space.
Federal tax credits in play
Heat pump water heaters and some tankless models qualify for federal tax credits and rebates. Check the current Energy Star website before purchase — credits can meaningfully change cost comparisons.