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Old 11-02-2011, 02:59 PM   #1
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expansion tank for 40 gal gas water heater


i was wondering if this is an adequate expansion tank for a 40 gal gas water heater:

http://www.houseneeds.com/shop/flexc...-htx30-buy.asp

or this:

http://www.amazon.com/Flexcon-PH12-E...0264266&sr=1-2

I am skeptical about the former cause it says "closed loop". that's the one i have for my closed radiator system and water heater system isn't closed, i guess. so maybe the latter.

thanks


Last edited by amakarevic; 11-02-2011 at 03:06 PM.
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Old 11-02-2011, 04:00 PM   #2
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expansion tank for 40 gal gas water heater


They look essentially the same but I'd go with the one spec'ed for potable water systems (the one linked on Amazon). Maybe the membrane is made of material certified to not leach anything into potable water supply whereas that may not be the case for the other one. Good to see you going with the 4.5 gal size. You could technically use the 2 gal size with a 40 gal water heater but with these the bigger the better as in less pressure rise as the water heater heats up.

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Old 11-03-2011, 07:12 AM   #3
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expansion tank for 40 gal gas water heater


Installed one half the size 20 years ago on my cold water inlet from the street never had a problem since then. Problem was water heater relief valve weeping due to no expansion capability.
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Old 11-03-2011, 11:12 AM   #4
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expansion tank for 40 gal gas water heater


I understand the codes in most places call for exp tanks on new construction. My place built in 1995 did not have one. After I was there for a year or 2 I installed a pressure gage and watched system pressure during a water heater heat up cycle. It got to well over 100 psi. And that wasn't even a "design basis" transient that would occur with heating up an entire tank of water from stone cold winter inlet temps. Yikes! I went out and got a tank that week from Lowes and installed it. No need to have every water heater cycle do a system hydrostatic test!
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