What is a water heater?

Look in the basement, the garage, a utility closet, or, in warm-climate houses, the attic. A gas unit needs a flue, so it stands near a chimney or has a plastic vent pipe running out a sidewall. An electric unit has conduit and a dedicated 30 amp double-pole breaker. Anything installed above finished space belongs in a drain pan piped to a drain. Read the label while you are there: it lists gallons, the first-hour rating, and a serial number whose first four digits usually encode the month and year of manufacture, which is how you learn the real age of a heater you inherited.

Cold water enters through a dip tube that carries it to the bottom of the tank, gets heated by a burner underneath or by two electric elements in the side, and rises to the outlet on top. Three small parts keep the whole thing honest: a sacrificial anode rod that corrodes so the tank does not, a temperature and pressure relief valve that vents if the tank passes 210 degrees or 150 psi, and a thermostat. Sediment on the bottom is the slow killer. It insulates the burner from the water, produces the rumbling or popping you hear during recovery, and the U.S. Department of Energy notes that scale buildup drags down efficiency. Once the tank shell leaks there is no repair, and a burst tank can release 40 to 50 gallons in minutes.

Four intervals cover a tank heater. Flush a few gallons of sediment out annually. Inspect the anode rod every 3 to 5 years, or every 2 in hard water. Trip the relief valve once a year to prove it is not seized. And hold the thermostat at 120 degrees, the Department of Energy recommendation, which trims standby losses and scald risk; the temperature setting guide handles the tradeoff at higher settings. Kept up, a tank finishes at the top of its 8 to 12 year range, and the replacement timing guide explains why swapping at year 11 beats swapping at year 13.