There was once a magazine called Appliance Magazine that conducted surveys to determine the average life expectancy of various appliances. Their 2005 study estimated that the average gas hot water tank lasts for 10 years and the average electric tank lasts for 11 years. This may seem like an old study, but the construction of a basic water heater has not changed much since then. However, there are several factors that can increase or decrease the life expectancy of your water heater.
Does your area have hard water?
If your home has hard water (which is water that is excessively high in minerals), it will cause scale to build up in your water heater. This will make it harder for the burners to transfer heat to the water, resulting in them running more often. This will decrease the life of your water heater, potentially by multiple years. However, flushing your tank annually to get rid of excess mineral buildup, and regularly checking and potentially replacing the anode rod (which is designed to attract corrosive substances and react with them before they can eat away at your tank) will help increase the life of your tank. Have a water softener is another way to prevent hard water from negatively affecting your tank.
If your home has very hard water, you will probably already know. If you are unsure of how hard your water is, you can look at this map of the United States to see how hard water is in your area.
Usage
The number of people using a water heater and the total number of times it is used per day will affect its life. Whenever a water heater is used the metal will expand as it is heated up. When it cools down later it will shrink back to it’s original size. You may even be able to hear popping or snapping noises as it cools down- similar to how an oven or furnace vents may crackle as they cool down. This expansion and contraction of the metal is what will eventually cause it to crack at some point.
Tank materials
Most water heaters are made out of inexpensive, non-stainless steel. This steel is then glazed with glass to increase its life. Unfortunately this glazing usually doesn’t last very long before it starts to develop cracks. If your tank is made out of stainless steel or another corrosion-resistant material, it should last much longer. These tanks are rare, however. They are usually found in commercial facilities or as part of boiler systems, where they are just empty tanks (known as indirect-fired water heaters) that are filled with water that is heated by the boiler.
How old is your water heater?
You can tell how old your water heater is by looking at the serial number. Each manufacturer has a different way of placing the date of manufacture within it. Normal hot water tanks have a warranty of 5-8 years against leakage.