The Basics

How Do Gas Water Heaters Work?

A gas water heater uses a method called convection to heat the water used for everyday needs. Convection is the process of cold water being injected into the water tank. Special hot water burners are located on the bottom of the tank. These burners heat the water, causing the warm water to rise to the top of the tank. This water is siphoned off through pipes and transported through your home plumbing to provide hot water wherever you need it. As the hot water on the top is siphoned off, new cold water is pumped into the tank, and the process repeats itself. How long your hot water lasts depends on how big your tank is and how efficient the burners work at heating the water.

Water Supply

The water heating process starts with your water supply. This is the same source of water for almost everything else in your house. The water source is connected to the tank by cold water supply lines. These lines are controlled by a special valve. This allows you to cut off the supply of water to the tank if needed for issues or repairs.


Most hot water tanks are made of steel. They are specially designed to be able to handle large amounts of internal pressure without exploding. The pressure is created by the physical heating of the water. Located at the bottom of the tank is the dip tube that shoots the cold water into the tank. The inside of the tank usually contains a sacrificial anode. The sacrificial anode is a special rod made of aluminum or magnesium that attracts corrosive properties to itself rather than to the tank. This prevents internal corrosion and damage to the tank itself.


The most important aspect of the gas water heater is the burner. Outside the tank there is a gas line that directly inputs gas energy to power the burners. As the burners run, they heat up the cold water inside the tank, causing the process of convection to start. The gas burners are controlled by a control module. This controls the temperature of the water, and it can also act as a scald guard. The burner is turned on using a pilot light. This ignites the gas and creates the energy needed to run the burners. The control module also controls the pilot light.


When natural gas is combusted (lit), it creates a series of combustion gases. The gases need to escape, and they must do so in a way that is not harmful to the inhabitants of the house. These gases escape through an exhaust flute going from the top of the hot water heater to outside the house.

Pressure Release

As mentioned before, the heating process of a gas water heater can cause a large amount of pressure. If too much pressure begins to build up inside the water tank, the pressure release gauge kicks in. This safety gauge makes sure that the pressure can be released safely when the tank begins to hold more pressure than it was designed to hold.


As the gas water heater is used, sediment begins to build up in the bottom of the tank. If this sediment is not periodically drained, it can cause your tank not to work as efficiently. It could eventually cause damage to your hot water system. The drain gauge allows for the periodic draining of the tank.