An anode rod is a component of a water heater that helps to prevent internal corrosion. The rod, often called a sacrificial anode rod, attracts the corrosive elements in water and allows them to dissolve it. This slows the corrosion of the tank's liner. Almost all water heaters have the rods, though some smaller tanks, such as recreational vehicle water heaters, may not. Homeowners can replace the anode rods when they begin to deteriorate.
When different types of metal are exposed to each other, usually there is an electrical flow of current between the metals. As hot water heaters have various metals, such as copper piping, steel tank walls, and brass fittings, they have erosion from the electrochemical reaction. Anode rods are made of aluminum, magnesium, or a combination of metals. The sacrificial metal is wrapped around a steel wire or thin rod. In a cathodic protection action, the sacrificial metal allows the electrochemical reaction to attack it instead of essential parts of the water heater.
Aluminum anode rods are very effective in areas that have hard water. Some people have concerns about the negative health effects of aluminum; therefore, experts advise that people not use water from a hot water tank for drinking or cooking. The owner's manual usually lists what type of rod the manufacturer used. Sometimes homeowners smell a sulfuric, or rotten eggs, smell from the hot water. Often installing an anode rod made of aluminum and zinc will dispel the smell.
Magnesium rods are the most common type. Where there is hard water, they are not as effective as aluminum rods. Generally, there are no known health problems with the magnesium rods.
Experts suggest that homeowners check the anode rod yearly or every two years. Usually a rod will last for five years, but many factors can change this. The quality of the water and the amount of water used are two major factors. Possibly the most important factor is softened water. Salts in the water create a higher electrochemical reaction and dissolve the anode rod at an accelerated rate.
The anode rod is screwed to the top of the water heater. A homeowner may do the inspection himself, following the instructions in the user's manual, or hire a plumber. If the rod shows exposed steel or has a calcium carbonate covering, the homeowner should replace it. If a corroded rod breaks off in a tank, it will fall to the bottom and may damage the tank's inner walls. This usually drastically shortens the water heater's life.