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Anatomy of a Gas Water Heater (Tank type)

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Tank Construction
Sacrificial Anode Rod for Water Heater

Sacrificial Anode Rod for Water Heater

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Construction of the Hot Water Tank
The tank jacket itself is made of steel and encloses a pressure tested water storage tank. Between the storage tank and the tank jacket is insulation to reduce heat loss of the heated water. It is a good idea to supplement the insulation by adding a fiberglass insulation tank jacket to the outside of the hot water heater. These are inexpensive and easy to install.

Inside the tank you will see a dip tube. The dip tube is where the cold water supply enters the tank to be heated by the gas burner. Since cold air and cold water is denser than hot air or hot water, the cold water sets at the bottom of the tank until it is warmed by the burner and heated enough to rise (through convection) to the top of the tank where the hot water hangs out. See, more physics...

In glass-lined tanks there will also be a metal rod in the tank, usually magnesium or aluminum) called a sacrificial anode. The anode rod is bolted and fastened to the top of the tank and extends deep into the tank. It's purpose is to draw corrosion to itself instead of the metal tank. Some models do not have a separate anode but combine the function of the anode with the hot outlet. Plastic lines tanks do not have an anode

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