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Mark Henley
Mark Henley, Journeyman Technician
Category: HVAC
Satisfied Customers: 3217
Experience:  UA Journeyman Pipefitter , HVAC, Refrigeration, DDC controls. 26 years.Commercial & residential
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What is the proper pressure for my boilers expansion tank.

Resolved Question:

What is the proper pressure for my boiler's expansion tank. I keep reading online that most new expansion tanks come pre-pressurized at 12 psi and that you should pump the pressure up to 15 psi. after installing it. However, Home Depot only had expansion tanks pressurized to 25 psi. I bought a 5 gallon 25 psi expansion tank and now I'm wondering if I can just screw it on or if I have to let some of the pressure out of it so it goes down to 15 psi.
Thanks.
Submitted: 7 years ago.
Category: HVAC
Expert:  Mark Henley replied 7 years ago.

Hi,

 

You want it to be 12 PSI when installed cold. It will cause the pressure to rise to about 17 when hot, that is the standard for a hot water system in a residential system unless your home is much taller than a normal two story home, pressure = height in the system 17 PSI is good for a little over a 30 rise to the highest point of the piping system.

 

Thanks

 

Mark

Customer: replied 7 years ago.
Do I now let the air out of it until it goes down to 12 psi or do I need to get a different tank? The directions with the tank only talk about connecting to a water heater, not a home heating boiler. Thanks.
Expert:  Mark Henley replied 7 years ago.

Hi,

 

OK sorry that's a tank for domestic water its different from a boiler tank. You need to get one for a boiler system.

 

Thanks

 

Mark

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