What is thermal expansion and/or why do I need a thermal expansion tank?
Thermal Expansion as relates to water heaters/boilers is an increase of the volume (or space taken up) by water within the unit, caused by heat. In other words, when water heats it expands or takes up more space. The excess volume of water, because of pressure created, will flow to the place of least resistance. Unless a faucet is open, generally this would be into the cold water pipe (this is why sometimes the pipe above the cold water inlet is warm for a few feet). In a closed system, the excess volume of water has no place to go and builds pressure within the unit. When the pressure reaches a certain point, a safety device called a Temperature and Pressure relief valve (T & P) will open relieving pressure. Over time (perhaps as little as months or as great as years) this increase and decrease in pressure, without the protection of an expansion tank, can weaken the tank causing premature failure. Generally what is seen is a drip to a stream of water from the T & P that continues unti
