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Gas Boiler Original 1-1/4" Supply Line Reduced to 1" and 3/4"???

rapco Member Posts: 1
I have a gas boiler in a main house which is also heating four attached row homes.
Unfortunately, the boiler system needs to be re-piped hopefully in Pex-A oxygen barrier pipe. This is due to deteriorating steel lines originally installed in 1960.

The supply/return (S/R) lines are 1-1/4” from/to the boiler. However, the supply line is reduced to 1" and even ¾” at the end of the row homes. Also, I noticed that some of the ¾” zone valves are also reduced to ½”.

Is there an advantage or not, that the new S/R lines are 1-1/4" throughout, and also increase the new zone valves back to ¾”?

The approx. total S/R line run distance from the boiler to the last row home is about 240', total loop approx. 520', not including the 3/4" distribution lines for the registers in each room approx. 35 registers plus some slant/fin baffles.

Thank you!


    EBEBRATT-Ed Member Posts: 14,543
    It all depends on the flow required. The bigger the pipe the more flow. But you need to know how much flow you need to decide that
  • Snowmelt
    Snowmelt Member Posts: 1,399
    1 inch line is good for 100,000 btu
    1 1/4 is good for 125,000 btu ( maybe a little bit more)
    It’s like 10 pounds of potatoes in a 5 pound bag .
    So if your boiler is Over 100,000 btu on your output you need 1-1/4
  • hot_rod
    hot_rod Member Posts: 20,809
    It could be piped reverse return and the pipe size would step down like that. On a run that long, good chance is RR
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream