A Thermal Expansion Tank is a requirement, by law, when your hot water heater includes a back flow preventer at your water main or a check valve anywhere in your plumbing system. If you have installed a circulation pump anywhere in your house, you have a check valve. Additionally, backflow preventers have become a more prominent addition to codes in various areas. Whenever water is heated, it expands. In the past, excess or expanded water would flow back into the public water system, however backflow preventers stop this from happening, creating a need for a place for that expanded water to go. For example if you have a 40 gallon hot water heater there could be an additional 1/2 gallon of water created even without any demand.
Typically, as a homeowner, your hot water heater is not something you look at or check on a regular basis. You install it (or have it installed) and forget about it until one day you have a problem! You may or may not notice a little water coming from your water heater. It could come from the temperature pressure relief valve in the form of just a few drips or a gush of water. The cause for leakage could be linked back to the expansion of the water in the tank and now it has nowhere to go. When hot water is heated, it expands. That expanded water needs somewhere to go. The purpose of a Thermal Expansion Tank is to act as an overflow for the excess water created by the water heating, maintaining safe expansion pressure. The Butyl diaphragm inside the steel tank keeps your potable water from contact with the steel and is sent back into the system when the call for hot water comes again.
The ST-5 includes a Fresh Water Turbulator - a patented diffuser that agitates the incoming water to keep it fresh and clean while its water-jet scrubbing action prevents sediment for collecting inside the tank.
Several Amtrol Thermal Expansion Tanks also have an InSight Indicator Cap that includes its patented sight glass that changes color when your expansion tank needs to be replaced! This alerts the homeowner and/or plumber before damage can occur. The sight glass will remain clear/white under normal operation. However, when it becomes discolored, it is time to replace your tank. The InSight Indicator Cap is located at the bottom of the expansion tank. Additionally, a patent pending Antimicrobial Liner utilizes safe, Silver Ion technology to neutralize bacteria on contact while it targets active micro-organisms. This compound is molded into the water reservoir lining and will last for the life of the tank.
A Thermal Expansion Tank, such as the Therm-X-Trol ST-5, can be added to your 40 - 50 gallon hot water tank (dependent on tank specifications) piping at any point in time, but if you are installing a new water heater a thermal expansion tank should be added! It will protect your water heater against thermal expansion.
Typically a Thermal Expansion Tank is a small metal tank - usually either 2.1 gallons or 4.5 gallons. The ST-5 has a tank volume of 2 gallons and is 8" in diameter by 13" high. Its is constructed of stainless steel with stainless steel connections. The ST-5 offers a maximum working pressure of 150 PSI with a factory pre-charge of 50 PSI and a maximum operating temperature of 200°F.
The thermal expansion tank is typically installed on the cold water line between the water heater and the backflow preventer.