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Separate circulator or zone valve for indirect?

TomTA Member Posts: 20
My home has a HW heating system (single zone) with a coil. As part of an overall replacement of the whole system I want to install an indirect HW heater; the radiators will still be on a single zone. Is there any compelling reason to go with using a separate circulator for the indirect versus using a single circulator and two zone valves? The cost differential for a second circulator versus zone valves really isn't important in the grand scheme of things; I'm more concerned with longevity and idiot-proof set-up. Would the use of two zone valves make the DHW priority wiring more straightforward?


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    It might depend on the pressure drop thru the indirect. I'd probably use a second circulator.
    For me, generally, 1 or 2 zones, circulators, 3 or more, zone valves.

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    Solid_Fuel_ManAlan (California Radiant) Forbes
  • Robert_25
    Robert_25 Member Posts: 540
    There is really not any difference in the wiring complexity, but you would have to find a circulator with an appropriate pump curve.  Once you determine the pressure drop through your existing heating zone and the new indirect you can see how it lines up against some of the popular circulators.  If one of the new ECM circulators is a match, that would be my pick...then you will have good performance and energy savings.
  • newagedawn
    newagedawn Member Posts: 586
    i personally prefer 1 circ and zone valves, for upto 140000 btu boiler and 3 zone valves, so if you have a boiler thats 140000btu one circ and 2 zone valves will work perfectly, an alpha pump will work great also with zone valves
    "The bitter taste of a poor install lasts far longer than the JOY of the lowest price"
  • motoguy128
    motoguy128 Member Posts: 393
    The ECM circulators have a pretty wide performance range on a constant pressure mode, should work well with zone valves. That’s the way I’d go if I added a hot water zone off my steam boiler. Just add 2 zone valves and a new zone controller. But realize that the Indirect flow will likely be a little lower when both are calling, but that’s probably OK since the Demand will likely exceed the boiler capacity anyway, and water temp will drop until it reaches equilibrium. Or at least that’s what should happen.

    Another option is to use domestic priority, so they the pump flow varies less.
  • Big Ed_4
    Big Ed_4 Member Posts: 2,835
    What type indirect being used ?

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  • clammy
    clammy Member Posts: 3,115
    I generally use pumps w checks and install Chks on both supply and return of the heating side of the tank ,set them up for priority and install a quality portable mixing valve , portable expansion tank and call it a day . The reason for the checks is that on a low temp system you may end up w thermal migration from the boiler water in the tank to the system side ,which may not effect the tank output but will cause your aquastat to cycle for domestic and on tanks which hold large amounts of boiler side water like turbomaxxs it will migrate . Just a pet peeve . It’s also nice to have your water tested for hardnesss and possible if needed add a soften or a scale stopping filter to correct the issue and if it’s hard add some isolation valves w purge set up so the indirect may be de limed if need be or just flushed occasionally .as for pumps over zone valves on some tanks you just won’t get the correct gpm and the cost really isn’t much of a difference . Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating