Expansion Tank and PEX - need opinions

[virvis]

I was all set and ready to order a fairly large (90 gallon) expansion tank for my pressurized system and spoke to a supplier with a different opinion.

My system will be:

eko 40
1000 gallons of storage (2 500 gallon propane tanks)
2500 lf of 1/2" pex mounted under the subfloor of the 1st floor
250 lf of 1" pex headers feeding the 1/2" loops

The supplier said I shouldn't need anything larger than a 10 gallon expansion tank because the PEX will expand with the rise in water temp. and will keep the pressure in the system in check. I never even considered this and was wondering if anyone is using a smaller expansion tank on their boiler (5-6 gallon?) with a similar setup described above.

thanks,
Jim

 

[stee6043]

Wow.....I've never heard such a thing proposed. My suggestion would be to do a little quick math and look at how much water is in your pex compared to how much is in your propane tanks. Even if your pex size were to "expand" from 1/2" to 1" (physically impossible) I still highly doubt you would have enough acceptance volume for the amount of water you have.

I have (2) 66 gallon expansion tanks on my system with 1000 gallons of storage. Probably a little overkill but not by much...

I'd do a little more reading on your pex. I have a very hard time believing it expands any significant amount.

 

[Huskurdu]

Wow.....I've never heard such a thing proposed. My suggestion would be to do a little quick math and look at how much water is in your pex compared to how much is in your propane tanks. Even if your pex size were to "expand" from 1/2" to 1" (physically impossible) I still highly doubt you would have enough acceptance volume for the amount of water you have.

I have (2) 66 gallon expansion tanks on my system with 1000 gallons of storage. Probably a little overkill but not by much...

I'd do a little more reading on your pex. I have a very hard time believing it expands any significant amount.

Too much expansion tank is better than not enough exp tank.

np

 

[3designs]

as a owner of a previous all Pex house i will agree that the pex does expand to acccomodate pressures as heat increases but not to the extent that he is claiming. theamount of pex you have would deal with a few gallons but not the expansion of 1000 gallons starting at 12 psi going from 110-180 on a regular basis. That equates somewhere above the 60 gal mark... here try this out . http://www.b2epc.com/software/tank.shtml

 

[Gooserider]

Sounds to me like you either need to find out what that guy is smoking, and get him to share or find out where he lives so as to make sure you aren't in the fallout zone when he tries to go orbital....

Gooserider