Understanding Water Heater Anatomy

Water heaters stand steady in a dark corner of the home, ready to deliver hot water anywhere in the house. We rarely give them the time of day. They’re usually so dependable, until, of course, they aren’t.

What makes a water heater tick? Understanding how these mainstays of comfort and convenience work is important when it’s time to get a new one installed.

Let’s get up close and personal and take a stab at understanding water heater anatomy.


The inner shell is a heavy, metal tank that holds anywhere from 40 to 60 gallons of hot water at 50 to 100 psi of pressure. The exterior of the water heater is wrapped in an insulation blanket, normally made of polyurethane foam. Over the insulation is another shell, normally the outer shell, wrapped again in insulation.


Water enters the heater through the dip tube, normally at the top of the tank, and travels to the bottom where it’s heated to the desired temperature.


The shutoff valve stops the flow of water into the tank. It is usually located on the dip tube, above the water heater.


This pipe allows the hot water to exit the water heater. It is located towards the top of the heater on the exterior.


The thermostat is a thermometer and temperature control device. This is located in the control panel, normally at the bottom of the water heater.


Electric water heaters use heating elements, which are inside the tank of the water heater. Gas water heaters use a burner under the tank and a chimney above the water heater instead of elements.


Near the bottom of the water heater is the drain valve. This valve is used to empty the tank should the elements need to be replaced, to remove sediment that collects in the bottom of the tank, or if the tank needs to be relocated or replaced.


This valve is used to keep the pressure in the water heater at safe levels. Should too much pressure build up in the water heater, this automatic valve will release pressure until it is safe again.


This rod is normally made of aluminum or magnesium with a steel core. This rod is usually suspended in the water to help keep erosion at a minimum.

Now you know the parts that make up a water heater. When water is brought through the drip tube into the tank, the water is heated to the temperature your plumber sets during installation. A temperature of about 120 degrees Fahrenheit is generally safe and will prevent scalding accidents.

Once the water in the tank reaches the prescribed temperature, it’s released through the heat-out pipe. The water is kept at pressure to ensure a fast delivery through your home’s pipes.

Apollo Plumbing, Heating and Air Conditioning offers water heater repair and installation. Contact us today to schedule a visit.

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