Like hot-air balloons, domestic water heaters rely on the principle that warm things rise. When a tap is turned on in a house, unheated water flows through a tube leading to the bottom of a large steel storage tank. As the tank fills up, electrical heating elements, or a burner at the bottom fuelled by oil or gas, warm the water to a temperature controlled by a thermostat.
Water decreases in density as it gets warmer and rises to an outlet at the top of the tank that is connected to the hot water taps. Cooler, denser water naturally sinks below the warmed water to the base of the tank and is heated up. A cycle is thus created that keeps hot water flowing while the heater is on and water is in the tank.
Unused water stays warm in the tank for some time because of insulation in the lining.
Conventional tank-type water heater parts
Inflow – Cold water enters through a dip tube and flows to a heat source at the bottom of a steel tank.
Thermostat — The temperature of the water is maintained by setting a thermostat that switches the heater on or off as required.
Water storage tank – The steel tank is lined with glass to prevent corrosion and is insulated to keep water warm for longer.
Exhaust flue – Gases produced during combustion in gas-fuelled water heaters have to be vented.
Heat source – Cold water is heated by electrical elements or a burner fuelled by oil, propane or another gas.