A hot water tank heater works by the principle of convection where heated hot water rises and cold water is lowered to take its place before being heated. Gas is used to heat the water at the bottom of the tank.
A tank water heater lets in cold water via a dip pipe, and as the water is heated, it becomes hotter and lighter. This natural occurrence together with the high pressure inside the tank causes the water to rise through the hot water outlet and be used. The tanks have a thermostat that controls the temperatures in the tank and governs the fuel delivery to the burner.
These hot water tanks are normally insulated to reduce the loss of heat to the environment, but this doesn’t entirely eliminate it. To compensate for this heat loss, the appliances periodically heat up the water even when not in use, maintaining a stable preset temperature.
A gas hot water tank can also have special features to aid in its functionality. A vent that collects fumes from the burner usually pipes the toxic gases through the roof. These tanks also have drain valves located at the base of the tank to drain the water tank and facilitate the flushing out of accumulated sediments.