Standard “tank type” gas water heaters are found in most homes and with just a little maintenance, usually provide years of trouble free operation.
How a Gas Water Heater Works
The gas water heater works by convection, which basically means that heat rises. Cold water is supplied into the bottom of the tank by a cold-water inlet pipe (the dip tube) and is controlled by a shutoff valve. The cold water is denser than warm water and so it remains at the bottom of the tank where it is heated by the gas burner. As the water heats up, it naturally rises and is drawn off by the hot water discharge pipe. The hot water pipe is much shorter than the cold water pipe ensuring that only the hottest water is being used from the tank. 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. Many options exist for gas water heaters, including the type of gas used, the amount of heat generated (referred to as Btu output), the altitude at which the unit may be operated, the type and sizing of the venting and different brands of water heaters.
The design and parts of a gas water heater
The Tank
A typical 40 or 50 gallon gas water heater consists of a tall cylindrical outer shell that encloses an inner, heavy metal, pressure tested, water storage tank containing a water protective liner. Between the outer shell and the inner is insulation to reduce heat loss of the heated water.
The Burner
The most important aspect of the gas water heater is the burner. The burner is centered under the bottom head and flue. Outside the tank there is a gas line that directly inputs gas energy to power the burners. You should note that this pipe has its own gas shutoff valve and know where it is in case of an emergency. Gas is ignited at the burner by the pilot light. The resulting combustion transfers heat to the water through the bottom head and the flue which heats 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 control module also controls the pilot light.
The Pilot Light
Most traditional gas water heaters have a standing pilot light that burns continuously. When the temperature inside the water storage tank drops below the set temperature, the thermostat triggers the gas flow to the main burner. In order for the gas valve to open, however, the thermocouple must signal that the pilot light is burning and hot enough to ignite the gas. Many newer, energy efficient water heaters have electronic ignition instead of a standing pilot light and thermocouple.
The Thermostat
A water heater’s thermostat controls the temperature of the water inside the tank. Normally, you can set the temperature anywhere between 120 and 180 degrees Fahrenheit. The water temperature setting recommended by most manufacturers is between 120 to 140 degrees Fahrenheit. This is hot enough to be efficient for household use, but not so hot that it can pose a scalding risk. If there are children living in your home, it’s wise to stay closer to the lower end of the range.
Setting your water heater to a lower temperature saves energy, too, and if you remember to put your water heater in vacation mode when you are away you’ll experience even more energy savings. Usually, the thermostat is located underneath a protective cover plate and has a knob or dial you can turn to set the temperature.
Safety Valves
For safety, all gas water heaters are equipped with a T&P valve (temperature-and-pressure relief valve). This valve opens if either the temperature or pressure of the water exceeds a safe limit. The valve is connected to a pipe that runs down the outside of the tank, ending about 6 in. from the floor.
Exhaust Flue
Gas water heaters also have a gas combustion exhaust flue. 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.