Water Heaters

If you own a house, you own a water heater. You probably don't spend much time thinking about the water heater until, one morning, you go to take a shower and there's no hot water. Then you probably think about it a lot.

Water heating is a thermodynamic process using an energy source to heat water above its initial temperature. Typical domestic uses of hot water are for cooking, cleaning, bathing, and space heating. In industry, both hot water and water heated to steam have many uses.

A water heater consists of the following parts, as shown in the figure above:

• A heavy inner steel tank that holds the hot water Typically, this tank holds 40 to 60 gallons. It has to be able to hold the pressure of a residential water system, which typically runs at 50 to 100 pounds per square inch (psi). The tank is tested to handle 300 psi. The steel tank normally has a bonded glass liner to keep rust out of the water. 
• Insulation surrounding the tank
• A dip tube to let cold water into the tank
• A pipe to let hot water out of the tank
• A thermostat to control the temperature of the water inside the tank (Many electric water heaters have a separate thermostat on each element.)
• Heating elements to heat the water (These are the thick electric elements similar to those you see inside an electric oven.)
• A drain valve that allows you to drain the tank to replace the elements or move the tank
• A pressure relief valve (This is an important safety feature that keeps the tank from exploding.)
• A sacrificial anode rod to help keep the steel tank from corroding