Expansion tank sizing and options


Old 09-22-16, 10:15 PM
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Expansion tank sizing and options

I need some verification that my numbers are correct. I have a system with about 140 gallons of volume, 120 gallon buffer tank and 20 gallons between two boilers(run in parallel) and the zones. I'm just starting to set up the second boiler and buffer tank and I wanted to make sure I size the expansion tank correctly. I was using the calculator on the watts site and it states that the acceptance volume should be 4.11 gallons. I already have an Extrol 30, 2.5 gallon, that was on the propane boiler and it is three years old. Should I just toss the 30 and get an Extrol 90 or run two 30s? I was going to run it on the output to the zones that is located on the top of the buffer tank as that is the highest point in the system besides the actual zones plus the lower velocity in the tank should aid in air removal.
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Old 09-23-16, 06:40 AM
Join Date: Oct 2008
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I don't think it would make any difference, performance-wise, using a single 90 vs. two 30s.

Modern doctrine is to connect the expansion tank at the suction side of the circulator pump..

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