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Pipe sizing for secondary loop

chris_93 Member Posts: 84
Hi, How do you determine the proper sizing for a secondary loop. Most new mod con boilers in 120-150k range have a 1 1/4" tappings for the primary loop. The buderus GB142 has 1 1/2" tappings.

1. Is a 1 1/4" secondary loop big enough to deliver all 150k btus.



  • Brad White
    Brad White Member Posts: 2,398

    Short answer is, yes, you can deliver 150 MBH though 1-1/4" pipe. At a 20 degree drop, 15 GPM will be in an acceptable range (a little higher than I would go, but then, I am conservative.)

    You could also deliver 300 MBH in the same pipe if you design for a 40 degree drop... it all depends.

    What is the basis for your emitter selection, delta-T, (flow and temperature in and out)?
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
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