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Side arm

SeanBeans Member Posts: 520
What are some side effects of having one pump for both, an indirect and 2 zones of heating.

Pump would be mounted on side of boiler pumping into return tapping.



  • Jamie Hall
    Jamie Hall Member Posts: 23,277
    OK I'm confused. Is this a hot water boiler? Or are we running a couple of zones and the indirect off a steam boiler?

    Either way you could use one pump and appropriate valves, but if this is a steam boiler and you are pumping into the return rather than a closed system, you are guaranteed to have cavitation problems on that pump.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • SeanBeans
    SeanBeans Member Posts: 520
    This is theoretical @Jamie Hall

    It would be a hot water boiler with two zones of heating and one priority zone of DHW.
  • Jellis
    Jellis Member Posts: 228
    2 zones + 1 indirect with 1 circ pump and 3 zone valves is a common system, there are no "side effects" as long as you design and install everything properly.

    I'm not sure I understand what you are asking.
    delta T
  • Zman
    Zman Member Posts: 7,569
    SeanBeans said:

    This is theoretical @Jamie Hall

    It would be a hot water boiler with two zones of heating and one priority zone of DHW.

    This is done all the time. It does not work all that well with a mod/con and outdoor reset.
    With a cast iron boiler you can use one circ and pipe straight through the boiler, no primary/secondary.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • delta T
    delta T Member Posts: 884
    The only reason I would have a separate pump for an IDWH is in the case of a P/S setup. Take the loop for the IDWH off before the secondary loop, so as to direct pump the idwh off the boiler without having to pass through any P/S piping. In that case you would need check valves to keep the flow where you want it. In direct piped systems though, a zone valve and a priority control works just fine. make sure your zone valve Cv is high enough to get the required flow for the IDWH though..
  • SeanBeans
    SeanBeans Member Posts: 520
    So in this photo is shows how the manufacturer recommends doing it..

    Now imagine taking both of those pumps out and only putting on pumping into the boiler..

    The reason for this question is that the books shows two circs in specific positions. but if we were to ignore their recommendations and whatever we wanted like a lot of installers seem to do.. what would happen?

    Everything works the same?
  • delta T
    delta T Member Posts: 884
    edited September 2019
    If you only put one pump pumping into the boiler, you will be effectively pumping towards the point of no pressure change assuming the expansion tank is where it is on the diagram.

    As to using one pump for multiple zones and using zone valves instead of zone pumps, it will be fine as long as the pump has the capacity to pump the heating zones at the same time, and the indirect by itself (assuming a priority control is used).
  • delta T
    delta T Member Posts: 884
    I might point out that the two diagrams are basically the same, just that with multiple heating zones, a reverse return piping system seems to be what they want. with a single heating zone and priority DHW reverse return is not necessary as they will never run together at the same time.