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.
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
A drawing of a water heater to label: write a name on the line for each number. Numbers 1 to 8 are the tank with its pipes, valves and rod; 9 to 13 the shell, the insulation and the flue.
Read the full guide
Word bank for the water heater worksheet
In alphabetical order, to copy onto the board: anode rod, cold water inlet, dip tube, draft hood, drain valve, flue, flue baffle, hot water outlet, insulation, jacket, relief line, tank, temperature and pressure relief valve.
The names that get swapped
Two pipes stand on top. The cold water inlet carries on down inside the tank as the dip tube; the other is the hot water outlet. The thin rod hanging in the water under its own small head is the anode rod. The zigzag inside the wide flue is the flue baffle. Outside in, the layers are jacket, insulation, tank. One side has two valves: relief valve high, drain valve low.
Number 6 has the longest name on the sheet. T&P valve is its short form.
Drawn without a number: the pipe above the draft hood, the burner under the tank, and the gas control valve with its pipe.
Questions and answers
What is the T&P valve on a water heater?
The temperature and pressure relief valve: a safety device that limits the temperature and the pressure in the tank. A probe that is part of the valve reaches into the stored water. The sheet draws that probe as a short line.
What is the pipe on the side of a water heater?
The relief line, also called the discharge line. It starts at the relief valve and runs down the outside of the heater, so that water the valve lets out goes toward a drain.
What is the draft hood on a gas water heater?
It is the cap that stands over the top of the flue. Its underside is open, and air enters the vent from below it. Some parts lists call it a draft diverter.
What is a glass-lined water heater tank?
A steel tank with a lining of glass bonded to the inside. The glass keeps the water from touching the steel, which protects the tank from rust. The drawing shows the tank as one shape and does not draw the lining.