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multi boiler pump opitions

clammy Member Posts: 2,740
Wondering what the general opion is on a p/s multi boiler installation .The exiting piping has a 2 .5 inch supply and return head with each zone having it's own pump .What i planned on doing is installing 4  300,000 btu boilers pipe them in a reverse return each with there own pump and aquastat/circ relay and flow checks and tie into the exiting piping with a set of tees .Does this make more sense then 1 large pump which will flow through all the  boiler wheather they are firing or not .The only real difference is that instead of just a aquastat on each boiler they would have a aquastat/circ relay which would fire the boiler and cyle the pump .The piping from the boilers to the tees would be minium at best .Are there any faults with design that i am missing exept for the stand by lose of constant flow .The boilers will be stage with a tekmar w outdoor reset .The rest of the building controls shall stay as is so far .The boilers are for heat only no domestic so far .Thanks for any thoughts peace and good luck clammy
R.A. Calmbacher L.L.C. HVAC
NJ Master HVAC Lic.
Mahwah, NJ
Specializing in steam and hydronic heating


  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    I am not a profesional, so

    think carefully about what I am about to say. The instruction book for a W-M Ultra 3 system with multiple boilers and primary secondary piping is shown on pages 54 to 60, especially pages 57 to 60. THe manual is here (.pdf):


    If you do not have a WM Ultra 3, there should be something like this in the I&M manual of the boilers you have.
  • Tim_Hodgson
    Tim_Hodgson Member Posts: 60
    It should work fine.

    The pumps and boilers need to be identical and make sure you have a check valve to prevent reverse flow through the other boilers when they are off.

    Good luck,

    Tim Hodgson
  • hot_rod
    hot_rod Member Posts: 16,334
    sounds like a good job for

    a separator. It will provide dirt, air, and hydraulic separation and ease of piping.

    it assures all pumps behave properly and much more. Size it to the required GPM, not necessarily pipe size.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • LarryC
    LarryC Member Posts: 331
    Why the reverse return piping?


    If each boiler will have its own circulator and check valves, do you need to pipe them in reverse return?  I thought the reverse return piping was used to help divide the flow among parallel paths, when you did not have some sort of individual flow control means.
  • clammy
    clammy Member Posts: 2,740
    just me

    Larry it is just the way i prefer to pipe multi boilers instead of direct return ,all things being equal it gives me peace of mind that all boilers see the same pressure drop and see the same return temp just a pet pev of mine .peace and good luk clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
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