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Expansion Tank | Tankless Pros Az | Phoenix, Az 


photo expansion tank cutaway

Whats inside the expansion tank

What is an expansion tank & why do I need one?


An expansion tank is a cylinder tank as shown above and is recommended for most standard home tankless water heaters and for traditional tank-type water heaters for most homes, and is typically now required for use on all water heaters.

Expansion tanks are built with a rubber bag (bladder) inside the tank and are about half the size of the tank itself, this bag is filled with air pressure that should match the pressure of the incoming water into your home's main water supply piping from a municipal water source, homes on private well are usually not required to have an expansion tank.


An expansion tank is required if a plumbing system is “closed”, which means that the back-flow device that normally runs between the house and the main water supply is now blocked at the meter or other locations by a check valve, this (check valve, pressure regulator, backflow prevention devices) allows water to flow from the water meter to your home but, not backward... blocking the extra pressure from thermal expansion of your water heater.  


When water is heated, it starts to expand the water up to an average of 20% or greater which causes a rise in water pressure, this increased pressure must go somewhere. If there is nowhere for the pressure to go, it places extra stress and strain on your water heater and your home’s plumbing system. It can also cause your water heater T&P safety valve to slowly leak allowing mineral deposits to collect and block or seize the valve. 


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