The importance of thermal expansion tanks

 

A thermal expansion tank is now required by code in most parts of Kansas City when replacing a water heater. The expansion tank is designed to help protect the water heater from premature failure due to thermal expansion.

"My old water heater didn't have an expansion tank and it lasted a long time, why do I need one on my new tank?"

The requirement of thermal expansion tanks is something that has slowly started to take throughout various parts of the city. Kansas City, Kansas was one of the first areas to require expansion tanks on all new homes built which was back in the late 90's. Kansas City Kansas is notorious for premature water heater failure. Part of the reason is due to the extremely hard water that if found in the area. The other contributing factor is the city water supply.

The city water supply can wreak havoc on water heater if certain factors are present. One of the biggest issues has to do with the way we protect our potable water supply. A backflow preventer is usually located in either the meter pit in the front yard. A Pressure Reducing Valve or PRV can also act as a backflow preventer by not allowing water to leave the house. Many of the newer homes in Johnson County have pressure reducing valves which creates a closed loop system. When any type of backflow preventer is present it is referred to as a closed loop system.

The problem with closed loop systems

The reason that closed loop system causes problems is from thermal expansion. When water is heated it expands at a rate of roughly 3% on a 70 degree rise. When the water can't escape the inside of your house this increased volume doesn't have anywhere to go and creates a pressure build up inside of the tank. This increased pressure can cause toilets to flush on their own, fitting failure, leaky faucets, and premature water heater failure. The expansion tank not only protects your water heater but your entire plumbing system.

An expansion tank will not last as most water heaters

While most water heaters have at least a 6 year warranty, expansion tanks often only carry a 1 year guarantee. Brands like Amtrol and Backstop are a little higher in price but carry 5 or 6 year warranty. An expansion tank is very easy to check, I can usually tell by tapping the side of the tank with my hand.

The inside of a thermal expansion tank has a rubber bladder that is filled with air, usually about 70 psi. If the bladder fails, the tank will become waterlogged and unable to protect against thermal expansion. A valve stem located on the bottom of the expansion tank, much like on a car or bicycle tire, which can be checked with a tire gauge. It's important to check your expansion tank on a yearly basis to ensure that it has not failed. This is especially important once your water heater exceeds the warranty period of the tank.