# How to size an expansion tank?



## bsybesma (Dec 8, 2009)

I'm working on designing a central plant. I know I need expansion tanks for my HHW and CHW loops but I need some direction on how to size them.

Any help would be much appreciated.

Thanks,

Brian


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## The Coastal Craftsman (Jun 29, 2009)

The people you buy your system from should be able to tell you what size expansion tank you need for your system size.


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## Tom M (Jan 3, 2007)

You're in HVAC and dont know how to size an expansion tank. There is an equation for this.


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## bsarrail (Dec 8, 2009)

Consult your vendor for appropriate sizing information.

Bell and Gosset has an excellent sizing manual for sizing pressurized expansion tanks with a membrane barrier separator between water and air side.

There are a few things you need to know before you begin sizing:
-total system water content
-average system design water temp
-minimum fill pressure (pressure to overcome height of building +4 to 5 psi)
-max operating pressure of system
-static pressure of system

Methods differ from manufacturer to manufacturer as well as tank configurations. Don't forget to check code requirements.


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## bm4branes (Feb 22, 2010)

4% of circulated volume


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## beenthere (Mar 5, 2009)

bm4branes said:


> 4% of circulated volume


Is that 4% of GPM. Or of GPH.
Since 4% of 600GPM is 24. And 4% of 36,000GPH is 1440.


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## bm4branes (Feb 22, 2010)

beenthere said:


> Is that 4% of GPM. Or of GPH.
> Since 4% of 600GPM is 24. And 4% of 36,000GPH is 1440.


Apologies, 4% of fill.


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## MrEngr (Aug 24, 2010)

*Here is a link that shows you how to size an expansion tank*

Look here, the forum is giving me a problem with posting a URL so you will have to take out the spaces.

www . engineermanual . com/index.php?title=23_21_16.13_Expansion_Tanks


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