If you have not received a letter from your local water supplier yet instructing you to install a thermal expansion device in your house or business yet, expect it soon. The letter states that due to upgrades in water supply systems that this device must be installed in a timely manner. I have received many phone calls inquiring what this is all about. So here is an explanation that should answer all your questions.
Local municipalities are installing a valve at all water meters called a back flow preventer. This is a valve which allows water to flow only one way, into your house. The purpose of this valve is to prevent foreign material from entering the public water supply. Lets say you are washing your car and your garden hose is in a bucket of soapy water, if the city water supply is interrupted a siphon can occur and will suck that soapy water out of the bucket, through the hose and into the water mains. When service is re-established that soapy water will be distributed to your house and all your neighbors houses. This is the upgrade they are talking about.
Now you are probably asking yourself' "How does this affect me?". Once this back flow preventer is installed at the meter your water system is now sealed meaning water comes in but does not go back out. Back to the point at hand, thermal expansion occurs in the hot water system. When water is heated in the water heater it expands. With a sealed system it has nowhere to expand to. A thermal expansion tank is a vessel about the size of a gallon of milk. This tank is charged with air at about the same pressure as your homes' water pressure and in the tank is a balloon. The thermal expansion tank is installed in your water supply system usually at the inlet side of the water heater. When water is heated and expands, the expansion takes place in the balloon not adding the increased pressure to your water system, and when it retracts the air pressure around the balloon pushes it back into the system safely. There are other types of expansion devices available but the tank has proved to work the best.
Thermal expansion devices are now required by plumbing code even if a back flow preventer has not been installed yet. They are usually installed when the water heater is replaced in older homes and should already exist in newer homes.
If you are unsure of the location or presence of a thermal expansion device in your home, contact a licensed plumber to inquire about it.
