Do I need a thermal expansion tank for my water heater?
Thermal expansion tanks provide a safe place for expanded water to go. Most water meters are installed with backflow prevention devices that can create a closed system. Pipes in your home may burst unless there is someplace for this expanded water to go.
About Water Heater Expansion Tanks
Virtually, every modern plumbing code requires the installation of an expansion tank on hot water heater installations. The reason is simple. Water expands when heated. This extra volume of water needs to go somewhere. Before the widespread usage of backflow preventers, check valves and pressure reducing valves, this expanded water simply pushed the cold water back into the city water main. If your house has one of the above mentioned devices, you could have problems. These devices prohibit the flow of water from your house back into the public water system.
Without an expansion tank, the expanding water can cause your hot water heater to possibly fail because of the increased pressure. This pressure can cause serious life threatening problems as well, if you heat your water with natural gas or propane. The water heater tank can collapse around the internal flue and cause carbon monoxide to enter your home. It is serious business.
Expansion tanks are really simple devices. They contain compressed air and a special rubber bladder. When your hot water heater turns on, the water within your piping system begins to expand. This expanding water enters the expansion tank. Eventually, hot water is drawn from the system thru a faucet and the expansion tank releases the extra water into the piping system.
Expansion tanks come in various sizes. The size you need depends upon two very important variables. You need to know the capacity in gallons of your water heater and the water pressure of your house piping system. The capacity of your hot water heater is stamped on a label or a plate on the side of your hot water heater.
Water pressures within municipal water systems vary widely. Here in Cincinnati, water main pressures vary from 50 pounds per square inch (PSI) to over 200 PSI within a distance of a mile! This same thing may be true in your city. People with cisterns or wells control their own system pressure thru the use of electric pumps.
It is easy to determine your incoming water pressure. Many plumbing supply houses sell a little gauge that attaches to any faucet which has garden hose threads. Or if you like, you can call your local water department. They will possibly send a technician to your house. This person has very accurate gauges which will do the same thing.
Once you have this information, visit a local plumbing supply house that sells these tanks. They will be able to provide you with the proper sized tank to suit your needs.
Be sure to follow the directions that are packaged with the expansion tank. It only takes a few moments to read them. This will insure that your tank will function properly.
If you install a pressure reducing valve to control water hammer, be sure to buy one with a bypass feature. Without this, your water heater will begin to malfunction. You will see water dribble out of the pressure/temperature safety valve without a doubt.
The reason lies in the fact that heated water expands. Without a pressure reducing valve, this expanded water can easily go right back outside to the water main. Low quality or malfunctioning pressure reducing valves block this backwards flow of expanding water.