When inspecting your water heater, you may notice that it has a small tank attached to the top of it. Known as an expansion tank, it’s a common feature of tank-style water heaters. So, why do water heaters have an expansion tank?
What Is an Expansion Tank?
An expansion tank is a small tank that’s used to store heated water. When heated, water expands. Water heaters have an expansion tank to store this heated, expanded water. They are about one-fifth the size of the main tank. Expansion tanks are used exclusively for storing heated, expanded water.
The Importance of an Expansion Tank
Tank-style water heaters need an expansion tank so that the heated water has somewhere to go. There are tank-style and tankless-style water heaters. The former heats water preemptively, whereas the latter heater water only when demanded by homeowners and their family members. With a tank-style water heater, an expansion tank may be required. The expansion tank will temporarily store the heated and expanded water.
Tank-style water heaters are designed to withstand pressure. Most of them operate at about 50 to 100 pounds per square inch (PSI). As they heat the water in the main tank, they will be exposed to more pressure. Too much pressure, of course, can cause a tank-style water heater to rupture or even explode. An expansion tank will protect against catastrophic failure such as this by providing a safe place for the expanded water.
Open vs Closed Loop Water System
Depending on whether your home has an open or closed loop water system, it may or may not have an expansion tank on its water heater. Only water heaters on a closed loop water system typically require an expansion tank.
Open loop water systems are characterized by their bidirectional direction of water flow. The water can flow into a home with an open loop water system, and the water can flow out of a home with an open loop water system. Closed loop water systems are different in the sense that water can only flow one way: into the home.
If you have a closed loop water system, your water heater won’t have anywhere for the expanded water to go. The water may become too hot to the point where it overpressurizes the main tank. An expansion tank offers a solution. With an expansion tank, the expanded water will be temporarily stored in the expansion tank. Therefore, the main tank won’t become overpressurized.