Expansion tank sizing

[muleman51]

I know this has been covered but I can't find or remember. I have 1000 gal propane tank and probably 35 gallons in the system. How much expansion room do I need. I'd like to put this all together with one pump. The only heat source on the system will be the Adobe.

 

[jebatty]

From 50F to 210F water expands just over 4%. I allow a 5% expansion factor. A 1035 gal system requires a tank with a minimum acceptance factor of 41.4 gallons (4%), and I would go a little higher. For example, and I'm not hyping this tank, the Amtrol SX-160V SX EXTROL Expansion Tank, 86 Gallon, has acceptance volume of 46 gallons. If you narrow the temp range, less expansion.

 

[2.beans]

i went with 4% and didnt have enough with probably 1100 gallons of water. im up to 55 gallons of expansion and thats just enough. i used a bunch of smaller tanks that way if one gets water logged i can change it and still leave the system running. that was my plumbers idea and seemed to make sense to me.

 

[Willman]

i went with 4% and didnt have enough

Could you elaborate on how you figured out the lack of x space ? I am picturing some rupturing of pipe or maybe worse. Another case of more is prolly better. Thanks.
Will

 

[MaineMike100]

i went with 4% and didnt have enough

Could you elaborate on how you figured out the lack of x space ? I am picturing some rupturing of pipe or maybe worse. Another case of more is prolly better. Thanks.
Will

Pressure relief valve should release the excess pressure to protect the system correct? I know we don't want the relief flowing all the time, but an occasional release is much better than damage to the system.

 

[2.beans]

mine would releive itself into my basement. so i keep adding expansion until it stopped. before i added my last tank (or tanks) it was just starting to dribble out of the relief valve when my water temp was at or near 170*.

 

[Willman]

Good to know. A good case for a new PRV .

Will

 

[jebatty]

Water expansion from 170F to 210F is about 1.5%, meaning 1035 system gallons will expand just about 16 gallons. If your pressure relief valve starts "leaking" at 170, you're going to lose a lot of water as your system temperature climbs above 170.

And the water you lose will be hot, and if it comes out with any force, someone could be hurt or worse.

 

[in hot water]

Call up a rep or dealer with sizing software to get the exact size. It's not best to count on relief valves to handle lack of expansion size. Then tend to dribble after a discharge or two, often times, for one thing.

Be sure to size to the highest temperature expected in a no power situation, not the 180F operating temperature.

 

[2.beans]

we used exact sizing computer hardware to figure it out, but sometimes hands on proves more than what you read or what you hear.

 

[SteveJ]

Using (broken link removed to http://www.watts.com/pro/divisions/watersafety_flowcontrol/support/support_ETsizing.asp), shows that for:

1035 gallons (water only)
Supply Pressure = 15 psi
Expansion tank pre-charge = 15 psi
Relief Valve = 30 psi
temp range from 90F to 200F

gives an
Expansion Factor = 0.03105

and the expansion tank should have a minimum
Acceptance Volume = 32.14 Gallons
Total Volume = 111.68 Gallons

So, other than the added expense are there any downsides to oversizing an expansion tank?

 

[BrownianHeatingTech]

So, other than the added expense are there any downsides to oversizing an expansion tank?

Added expense in the future if/when it fails. Difficulty of getting a replacement in a timely manner.

Joe