TankA steel vessel with a glass lining that stores the hot water.
Cold water inletWater from the supply line comes in here.
Hot water outletHot water is drawn off the top of the tank.
Dip tubeIt carries the cold water down to the bottom of the tank.
Drain valveIt lets the tank be emptied and sediment flushed out.
Temperature and pressure relief valveIt opens if the water gets too hot or pressure too high.
Relief line (discharge line)It carries anything that valve lets out down toward a drain.
Anode rodA magnesium rod that protects the steel tank from rust.
JacketThe sheet-metal outer shell that covers the insulation.
InsulationIt slows the loss of heat from the stored water.
FlueHot gases from the burner rise through it and out the top.
Flue baffleA metal strip that hangs inside the flue.
Draft hood (draft diverter)Room air enters the vent from below it.
Burner and gas control 6
BurnerGas burns here, under the bottom of the tank.
Combustion chamberThe enclosed space under the tank where the gas burns.
Gas control valve (thermostat)It feeds gas to the burner when the water cools.
Gas supply lineIt brings fuel gas from the house piping to the heater.
Pilot burner (pilot light)Its small flame lights the main burner when heat is needed.
ThermocoupleIts tiny current keeps the gas valve open while the pilot burns.
Electric heater 4
Upper heating elementAn electric rod that heats the water near the top.
Lower heating elementIt is immersed low in the tank.
Upper thermostatIt runs the upper element, then passes power to the lower one.
Lower thermostatIt turns the lower element on and off.
How this list was compiled: Every name checked on 2026-09-30, a name kept only where two independent sources use it. A water heater maker's service handbook for residential gas and electric heaters, full text on archive.org (https://archive.org/details/a.-o.-smith-gas-water-heater-manual); a second, unrelated maker's gas water heater manual with its parts list (https://archive.org/details/manualsbase-id-595776); US Army field manual FM 3-34.471, Plumbing, Pipe Fitting, and Sewerage (2001), chapter 5 and its figures 5-4 and 5-5 (https://archive.org/details/FM_3_34_471_P_2001); US Department of Energy, Energy Saver, Storage Water Heaters (Internet Archive copy, https://web.archive.org/web/2025/https://www.energy.gov/energysaver/storage-water-heaters); Wikipedia, Thermocouple and Pilot light (https://en.wikipedia.org/wiki/Thermocouple, https://en.wikipedia.org/wiki/Pilot_light). Licence: own work
The drawing: Drawn for this site on 2026-09-30 from plain geometry; a schematic of no maker's product, nothing traced. Licence: own work
How it works
The parts of a gas water heater are a steel tank wrapped in insulation, a burner underneath and a flue up the middle. The first drawing cuts one open. The second enlarges the burner, and the third shows the elements of an electric heater.
Read the full guide
Parts of a hot water heater, top to bottom
Cold water comes in at the cold water inlet and runs down the dip tube to the bottom of the tank. Hot water leaves from the top at the hot water outlet. The anode rod hangs in the water. The flue runs up the middle to the draft hood, with a baffle inside it. On the side are the relief valve, its line and the drain valve.
The burner and the gas control valve
Under the tank, in the combustion chamber, sit the burner and the small pilot burner. The thermocouple has its tip in the pilot flame. Outside, the gas supply line ends at the gas control valve, which holds the thermostat.
An electric heater has no burner, flue or draft hood. Two heating elements reach into the water, each with its own thermostat.
Questions and answers
What are the parts of a gas hot water heater called?
Outside: the jacket, draft hood, relief valve, drain valve and gas control valve. Inside: the tank, dip tube, anode rod, flue and baffle. Underneath: the burner, pilot burner and thermocouple in the combustion chamber.
What does the dip tube do?
It carries incoming cold water down to the bottom of the tank, where it is heated. Hot water is drawn off the top.
What is the anode rod for?
It is a magnesium rod that hangs in the water and protects the steel tank from rust. The rod itself is slowly dissolved as it works.
Which parts of a water heater gas and electric models share?
The tank, insulation, jacket, cold water inlet, dip tube, hot water outlet, anode rod, relief valve and drain valve. An electric heater has two heating elements and their thermostats where a gas heater has its burner and flue.