A water heater expansion tank is a smaller tank usually installed next to the regular water heater for the purpose of compensating for the thermal expansion caused by the heating of water. Expansion tanks are engaged when there is increased pressure from the heating water. They are filled with compressed air, and allow water to backflow into the tank until a sufficient amount hot water is released upon being needed. Then the air inside the tank pushes the excess water back into the tank.
Your Water Heater System
Universally, water heaters have both a cold-water line going into the tank, and a hot water line coming out of it. Traditionally, this system was an “open system” which means that water could flow both ways and thermal pressure build-up meant that many times this was the case. However newer systems are called “closed systems” which alludes to the fact that there is a precautionary check valve on the side of the cold water line to prevent water flow being transmitted back out the wrong end. This prevents water that could potentially be contaminated from flowing back into the water source, whether it be a well or city main water line.
Now check valves are necessary and produce good by-products, but they also are not forgiving for thermal expansion and pressure that results from the heating of water inside the tank. With water heaters you have cold water going in and hot water coming out, but in between there is a temperature increase that causes a thermal expansion, and therefore an increase of pressure within the tank.
Every water heater comes with a pressure release valve that allows for water release from the tank upon reaching sufficient psi. This is a safety feature to prevent pipe breakage or other hazardous pressure concerns. The problem is that the pressure release valve is typically insufficient for the demands caused by the continuous heating, cooling, and re-heating that happens inside the conventional water heater.
Thermal expansion negatively affects your pressure release valve and water heater system in the following ways:
Expansion tanks resolve the thermal expansion and increased pressure phenomenon by absorbing excess water into the extra room the tank provides. Tanks are filled with an air cushion that gives enough room for water to overflow into the tank, while allowing for a release upon the request of your plumbing appliances and fixtures at the other end of the water line. They are usually installed right beside the water heater in an upright position with a T-Connector on the cold water line. You can really install expansion tanks anywhere on the water line, but it is recommended that it is placed on the cold-water line rather than the hot water line. Contact Inland Empire Plumbing to see about getting a water heater expansion tank to increase the lifespan of your water heater, plumbing, and water fixtures.