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How gas hot water system works

  • 21 Jul 2021
  • Posted By Mitchel Plumbing Gas

When it comes to hot water in the house, most people just want the heated water. They don’t bother asking, How does a water heater work. But it’s a good idea to understand how your hot water heater works.

A water heater includes a tank where cool water is warmed and where hot water is stored. Some water heaters are fueled by electricity, but others use gas. If you’re wondering, “How does a water heater work with gas,” this explainer will walk you through the process.

A gas water heater uses convection. Cooler water enters the tank through a pipe. This pipe provides a constant supply of water ready to be heated for use in the home. Cooler, dense water at the tank’s bottom is heated by a gas burner below the sealed tank. The warming water rises to be discharged through a pipe at the top of the tank into the home. The tank’s gas burner is governed by a thermostat that monitors water temperature inside the tank, turning the heat source on and off as needed. Exhaust fumes from the gas burner escape through a flue that runs outside the home.

As you can see, there are numerous parts associated with a gas water heater and numerous possible repairs that could be needed if it stops working. This underscores the importance of hiring a professional to repair any issues you may have with your gas water heater and to perform hot water heating system maintenance.

Now that you understand the basics of a gas how water heater system, let’s dig a little deeper into the different components to understand more about its operation.


Most people are familiar with hot water heater tanks. There are tank-less systems that are more expensive that use a different process to heat the water for the home. But the traditional water heater has a 20 or 40-gallon tank that sits in a utility closet or in a garage. There is more to the heater system than just that tank.

First, a gas water heater has a sealed, pressure-tested water storage tank that has a steel outer jacket that wraps around it. The steel jacket is what most of us associated with the tank, but inside is the sealed water storage tank. That storage tank is wrapped with insulation to help reduce heat loss. At the center of the tank is a flue that rises through the top of the outer tank and sends fumes through a vent pipe outside the home.

Internal components

In addition to the tanks, a gas hot water heater also has other parts that help produce warm water safely. Some tanks have a metal anode rod that helps keep rust away. The rod, known as a sacrificial anode, attracts ions, keeping them from causing rust in the metal tank.

As noted earlier, a cold water pipe provides a constant supply to the tank and a hot water pipe delivers the heated water to the home. The cold water pipe is controlled by a shutoff valve, which can be used to shut water off to the tank during maintenance. When the valve is shut off, the water flow that provides pressure that keeps the hot water running out also is affected. Some tanks also have a shutoff valve for the hot water pipe to stop the flow of hot water into the home.

At the bottom of the tank is a gas regulator and burner. The natural gas or propane used to heat the water comes through a pipe that has its own shutoff valve. This shutoff valve can cut off gas to the water heater and can be used to turn the gas off when working on the system. But again, this system is not your typical do-it-yourself repair. It’s best to leave that to a professional. The gas line fuels the heating mechanism for the hot water heater, which also has a thermostat to monitor heat and help keep the water warm. Gas water heaters also have a pilot light that ignites the burner when the water drops below a certain temperature. The gas burner assembly provides the flames that heat the water at the bottom of the tank. Another component, known as a flame sensor, is a safety feature that prevents gas from flowing out of the burners when the pilot light is not lit.