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Primary/secondary spacing question

Chris_51 Member Posts: 60
I’m finalizing a two boiler system with primary secondary piping. The spec in the manual (buderus) calls for a maximum of 12 inches between the send and receive piping to the loop (2 inch). My spacing is 12 inches from the insides of the pipes, which is around 14.5 on centers. Basically its straight up from of each of the send return pipes of the boilers.

Is this close enough? If not, why? I could get them closer with another day of re-piping, but it would add more 90s and more overall fittings.



  • jerry scharf_3
    jerry scharf_3 Member Posts: 419
    no absolutes


    The rule of thumb is 6 diameters, thus 12" for 2" pipe. The truth is that this is a guideline rather than an absolute. The goal is to have the secondary flow hydraulicly decoupled. The closer the tees are, the less change in pressure between the two tees on the primary to unbalance the secondary. If you know the max flow rate, you could compute the drag over 14.5" vs 12" and figure out exactly how much extra drag would be involved.

    Or you can take my guesstimation that you will be just fine. Those of us who put ball valves in between the tees to power purge are far worse off than your extra 2.5".

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