How a Gas Tank-Type Water Heater Works

How Water is Heated

The key components involved in heating water in a gas tank-type heater include:

  • Burner – This is where combustion of natural gas or propane takes place. The burner lies at the bottom of the tank.
  • Flue – Also called a vent pipe, this takes away exhaust gases produced by the burner.
  • Pilot light – This small flame ignites the burner when heat is required. It allows for quick heating without the need for relighting each time.
  • Thermocouple – This safety device shuts off gas flow if the pilot light goes out.
  • Gas valve – This regulates gas flow into the burner.
  • Blower – Provides oxygen to the burner for efficient combustion.
  • Heat exchanger – Transfers heat from the burner flame to the water.

Here is the basic sequence of operation:

  • Gas flows into the burner and is ignited by the pilot light. This creates flames in the combustion chamber.
  • The blower provides oxygen to allow for full combustion.
  • The resulting hot gases pass through the flue and out of the tank.
  • The heat exchanger transfers heat from the hot gases to the water stored in the tank.
  • Once the water reaches the desired temperature, the gas valve shuts off the gas supply. The pilot light remains on.

This cycle repeats each time your hot water is used and the tank needs heating. The thermostat controls the gas valve based on the water temperature.

How Hot Water is Stored

The storage tank is lined with an enamel coating that prevents rusting. At the top and bottom are pipe connections for incoming cold supply and outgoing hot water.

Cold water enters the bottom of the tank. As it gets heated, the hot water rises to the top while colder water falls to be heated. This allows for a uniform water temperature in the tank.

An outlet pipe delivers hot water from the top of the tank to your home’s plumbing system when a hot water tap is opened. The volume of stored hot water depends on the capacity of the tank – usually 30 to 50 gallons.

Heat Traps – Preventing Heat Loss

A gas water heater loses some heat through the pipes connecting it to the home’s plumbing. Heat traps help minimize this wasteful heat loss.

They are simple, U-shaped pipe arrangements that retain hot water in the tank. By preventing thermo-siphoning, they can increase efficiency by 2-4%.

Most new gas tank heaters have factory-installed heat traps. You can add them to existing systems as a DIY project to save energy.

How Energy Efficiency is Maximized

Modern gas water heaters incorporate various design features to increase energy efficiency:

  • Insulation – Tanks have 2-3 inches of foam insulation to retain heat. This allows for minimal standby losses.
  • Flue baffles – These force hot gases to take a longer path for better heat transfer to water.
  • Intermittent ignition – The pilot light shuts off when not needed, reducing gas usage.
  • Enamel Glass Lining – This specially formulated glass coating prevents corrosion and rusting of the tank from within. It also retains heat effectively.
  • Powerful burners – Improved burner designs increase combustion efficiency. This allows faster heating with less gas.
  • Enhanced diagnostics – Advanced control boards monitor all aspects of the system for optimum performance.

Safety Features

Gas tank water heaters come equipped with many safety features:

  • Flame arrestor – Prevents flames or sparks from entering the tank.
  • Fusible link valve – Shuts off gas if excessive temperatures are detected.
  • Thermocouple – Shuts off gas when the pilot light goes out.
  • Temperature & pressure relief valve – Safely vents out excess heat or pressure buildup.
  • Gas control valve – Prevents gas flow if the pilot light is out.
  • Insulated pipes – Reduces risks of accidental burns from touching hot pipes.

Proper installation is also critical for safety. Vents and combustion air supply must be per code to avoid carbon monoxide hazards. Regular maintenance like annual checks and flushing will also keep your heater running safely.

Frequently Asked Questions

Here are some common questions homeowners have about gas tank-type water heaters:

How long do gas water heaters last?

The average lifespan is 8-12 years. Regular maintenance can maximize longevity to up to 15 years.

What temperature should it be set to?

120°F is ideal. Lower temperatures can breed bacteria. Higher than 130°F wastes energy and poses scald risks.

What causes the pilot light to go out?

Strong drafts, high humidity, spider webs, dust or improperly sealed vent pipes are common culprits. A blocked thermocouple can also extinguish the pilot.

Why does hot water run out quickly?

Frequent cycling, leaky fixtures, sediment buildup, a large family or undersized tank are possible reasons. Flushing the tank or upgrading to a larger model can help.

How do I light the pilot?

Turn the gas control knob to pilot. Hold down the reset button while holding a flame to the pilot hood. Once lit, hold the button 30 seconds before releasing.

What color should the flame be?

The pilot and burner flames should burn steadily with a sharp blue color. Yellow or orange flames indicate combustion issues.


Gas tank-type heaters provide reliable and efficient hot water for households. Heating water involves combustion of gas that transfers heat through a heat exchanger to water stored in an insulated tank. Several design features improve safety and energy efficiency in modern units. With proper installation and maintenance, a gas tank water heater can provide hot water for many years!