Anatomy of a Water Heater

By Kealia Reynolds

Your home’s water heater provides clean, warm water to allow you to wash dishes, do laundry, and take a shower. Learn about the anatomy of a water heater—from the outer shell to the internal heating mechanisms—and how the different parts come together to heat the water in your home.

The outer tank

The tank

The tank itself is typically made of steel and can hold anywhere between 40 and 60 gallons of water. Your water heater tank will probably be in your basement or laundry room.

Tank insulation

The exterior of your water heater is wrapped in tank insulation, which prevents warm water from losing heat. To supplement tank insulation, an inexpensive fiberglass insulation tank jacket is sometimes added to the outside of the water heater.


With an electric water heater, a thermostat monitors the temperature of the water inside the tank.

With a gas-fired water heater, there’s a temperature reader that’s inserted into the tank to determine when the water needs to be heated. Once the water reaches the specified temperature, the gas burner valve is turned on, introducing gas to the pilot light and kickstarting the process of warming the water.

Heating the water

Upper/lower heating element

Electrical water heaters will have a heating mechanism inside the tank to heat the water. These upper and lower heating elements will stay warm until the water reaches the correct temperature. Gas water heaters use a burner, instead.

Gas burner assembly

These parts are specific to a gas-fired water heater.

Gas shutoff valve

The natural gas or propane used in a water heater is supplied through a pipe with its own gas shutoff valve. This valve, usually located where the pipe first enters the house, stops gas from coming into the system.

Gas burner control

This serves as a type of thermostat for the water heater and controls the ignition of the pilot light. Once the water in the tank gets to the right temperature, the gas burner control will kick on the gas burner valve and introduce gas to the pilot light.

Pilot light

The pilot light serves as a small ignition flame for the gas burner. When it goes out, your heater or furnace may fail to operate. The gas flame should be about ½ inch in height and have a blue tip.

Exhaust flue

This part exhausts combustion gases from the burner and helps heat water in the storage tank. This structure must be properly attached to the outside of the tank and meet certain code requirements.

Tank Valves

Temperature/pressure relief valve

This safety device keeps pressure and temperature inside the water heater within safety limits. It’s located on top of the tank.

Drain valve

This valve, located at the bottom of the tank, empties the tank of excess water or sediment that builds up over time. By emptying your tank and getting rid of sediment, you can prolong the life of your tank and improve water quality. It will take about 45 minutes to an hour to drain a 50-gallon tank.

Product of the Water Heater

Hot water discharge pipe

Once the water inside the tank is hot enough, the hot water discharge pipe supplies water to various parts of your home. This pipe is suspended toward the top of the tank, next to the cold water supply line.

Overflow pipe

This pipe discharges excess or leaking water safely, preventing flooding and water heater damage. This can prevent the actual tank from overflowing.

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