Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Boiler flow

Jason_13 Member Posts: 304
I installed a cast iron boiler with two heating zones and an IWH. My concern is the boiler is about 42k. When I did the heat loss I need about 25K in one zone and 15k in the second.

Cast iron boilers should operate with flows between a 20 - 40f delta-T. That means this boiler should operate with a 2 - 4 gpm flow.If I look at the delta-T I see a delta-T of about 8-10f. I have a taco 007 and 2 Taco zone valves for heating and a 007 for the IWH. The hot water works fine but I am concerned about the flow through the boiler for heating. Should I reduce the flow with the gate valves on the returns to the proper flow?


  • Jamie Hall
    Jamie Hall Member Posts: 23,675

    throttling is certainly one way of increasing your delta T.  Not the best way, perhaps -- a different pump might be better -- but it will work.


    Don't use a gate valve for throttling!  They are meant to be either open or closed, and operating partly closed doesn't do them any favours.  You could use a globe valve instead -- although the head loss might be too high -- or a plug or ball valve.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • heatpro02920
    heatpro02920 Member Posts: 991
    Why not

    use bumble bees? Set them for your desired delta, there are rebate available to help with cost and they save some electricity too..

    Another option is a flow restrictor like the watts p3 {I believe they make 3/4" versions}, I have never used them in this fashion, I normally use them on tankless water heaters but it should slow the flow, I dont like using restriction to slow pumps though, I would much rather see a delta t circ in there..
  • hot_rod
    hot_rod Member Posts: 22,505
    the ∆T will move around

    that is common, and desirable.

    Does the amount of radiation match the boiler output?

    How does it run on a design day? It will reach thermal equilibrium at some condition, and it's the load connected to the boiler that dictates that temperature condition, regardless of where the boiler settings are.

    The circ needs to be sized to more the appropriate flow at design conditions, gpm feet of head.

    The months PM mag has an excellent article on this topic.

    Also Idronics 12 has some good info regarding thermal and hydraulic equilibrium that all systems operate under.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • SWEI
    SWEI Member Posts: 7,356
    Proper sizing is key

    as HR mentions above.  Most indirects we see are overpumped just like the rest of the systems are.  Contrary to what most plumbers seem to believe, a 007 is not the only pump on the shelf.  Consider a 005 or 006 instead.  Smart circs are marvelous, but really makes the most economic sense when they run for long periods of time.