Expansion Tank Size

[strmh]

Working on my install.....which at the moment will not have storage.

At some point, I plan to have 1000 gal storage.

My question:

Can I install an expansion tank now that will support the future storage? Will it hurt anything to have an oversized ET?

BTW....using some online calculators, I come up with a 60gal tank for boiler and 1000 gal storage. Doest that sound about right???

 

[trehugr]

It is a good idea to size your tank for the size of your future system, and no it will not hurt a thing. The experts however will suggest the proper placement of your expansion tank.

 

[jebatty]

Expansion tank mfr's often provide exact sizing information. A useful rule of thumb is 4% of total system water volume. Be sure to size based on tank acceptance volume.

 

[strmh]

OK, thanks to you both....

60 gallons puts me at about 5% of total volume......

Looking at nofossil's diagram for the Simplest Storage, he shows expansion tanks at each boiler, plus a larger one with the storage....

My storage will be right next to the boiler, so I'm assuming the one ET can serve both?

 

[sdrobertson]

My storage will be right next to the boiler, so I'm assuming the one ET can serve both?

I'm running one large expansion tank with no problems. I used a steel 330 gallon tank and my father used a 250 gallon propane tank.

 

[Robby]

I am not an expert. I followed wholesalers info and installed a Watts ET-90 in my system. Boiler 42 gal, storage 150 gal and about 14 gal in the lines. Not even close to big enough. Had to bleed off pressure as temperature came up. As it runs continous now until spring I left it like that, and as long as temp stays between 130F and 190F pressure is fine. ET-90 is 13 gal volume and 8 gal acceptance.

The Watts web site has a formula to size tank:

(broken link removed to http://www.watts.com/pro/divisions/watersafety_flowcontrol/support/support_ETsizing.asp)

I am adding just over 1000 gal storage in the spring and am adding ETSX-160 expansion tank which is 81 gal volume and 32.6 acceptance. The wholesale cost is just over $400. After long talk with knowledgable hydronics tech this is still minimum. Next tank up is a fortune. You can add multiples though.

If anyone disagrees, don't jump on me, take it up with Watts

Robby