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

 

An expansion tank is a cylinder tank about 2.2 gallons in size, and is typically now required for use on all water heaters from up to 50 gallons, larger expansion tanks for larger water heaters. They are also used for the installation of tankless water heaters.

 

Expansion tanks are built with a rubber bag (bladder) inside the tank and is about half the size of the tank it self, 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 municiple 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 devise 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, back flow prevention devices) allows water to flow from the water meter to your home but, not backwards, 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 8% 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 heaters T&P (temperature & pressure) safety valve to slowly leak.

 

Increased water pressure will shorten the life of all plumbing faucets, solenoid valves (such as the plastic valves found in ice makers, dish washers and clothes washers). However, expansion tanks provide relief from this excess water pressure by absorbing the extra pressure and expanded water thus protecting your home.

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Pressure in your expansion tank should be equal to the whole house water pressure, measured at the hose-bib, if your city or well pressure coming in to your home measures at 62 PSI then you should increase the expansion tank pressure via schrader 

valve at the top of the expansion tank to 62 PSI as well, most expansion tanks are factory pressured at 40-45 PSI.