Contrary to common belief, not all water heaters have a single thermostat. While some of them do have a single thermostat, others have two thermostats.
Water heater thermostats are temperature-controlling devices. They allow you to change the temperature of the stored water. A typical water heater thermostat consists of an adjustable dial. Turning the dial in one direction will lower the temperature of the stored water Turning the dial in the opposite direction will raise the temperature of the stored water.
Tank vs Tankless
There are two primary styles of water heaters: tank and tankless. Tank-style water heaters feature a tank. They work by heating and storing water in a tank. Tankless-style water heaters, as the name suggests, don’t have a tank. They heat water on demand as it enters your home.
Both tank-style and tankless-style water heaters use thermostats. Tank-style water heaters, though, may feature two thermostats, whereas tankless-style thermostats typically only feature a single thermostat.
Heating Elements
Many tank-style water heaters – particularly those powered by electricity and not natural gas – feature two thermostats because they have two heating elements. They have a heating element at the bottom of the tank and another heating element at the top of the tank. Rather than featuring a single thermostat to control both heating elements simultaneously, they feature a separate thermostat for each heating element.
If you have a tank-style electric water heater, you may discover that it features two thermostats. The thermostats will be located at the top of the tank and the bottom of the tank. Adjusting the top thermostat will change the temperature of the top heating element. Adjusting the bottom thermostat will change the temperature of the bottom heating element.
Why don’t tank-style water heaters use a single heating element exactly? The reason is efficiency. With a single heating element, they’ll have to consume more energy. The heating element will draw more electricity as it attempts to keep the stored water warm. With two heating elements, though, tank-style water heaters are more efficient.
Most tank-style water heaters don’t use both of their heating elements all the time. They’ll typically use the bottom heating element to warm the incoming water. The newly warmed water will then float to the top. Since it’s already warm, they won’t have to activate the second, top heating element.
Tank-style water heaters will only use the top heating element when the temperature in that area of the tank drops below that of the thermostat setting. If you take a long hot shower, for example, the top heating element will activate. If you don’t use a lot of hot water, conversely, only the bottom heating element will activate.