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Mixing Valve/Dirt Sep/Circ Placement Location Help

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kh7
kh7 Member Posts: 3
edited 12:56AM in THE MAIN WALL

I have an Burnham ES2 boiler, 1-1/4" piping near boiler, Grundfos Alpha 15-58 circulator, two zones, one priority DHW and one heating zone, cast iron radiators, gravity conversion.
I am moving my boiler and repiping it and hoping to make some improvements from last year.
Last year I added the Caleffi 577 XF dirt sep, the Caleffi 280 ThermoProtec, and put the air sep on the main loop (it was previously on the heating loop only).
This configurationis shown in image 1, with the circulator on the supply, down stream from the air sep/expansion tank/fill.
After adding the mixing valve I get some short cycling which I am hoping to alleviate.
The ThermoProtec mixing valve has the 115F degree cartridge in it, as it is the lowest Caleffi makes. The ES2 boiler is rated for 110F return temps and this cartridge doesn't fully open until until Tset +18F so 133F.
Caleffi ThermoProtec documentation says the circ should really be pulling through the mixing valve instead of pushing into like I did.
Their documentation image 2 shows the circ pulling through the mixing valve and pumping directly into a dirt sep, though this is with P/S ping and a hydraulic separator upstream of the mixing valve.
I have drawn up three other designs based on the desire to pull through the mixing valve but am 1. unsure which of these designs is best, and 2. unsure if it will help the short cycling either way.
Oh and the TRV shown in the diagrams do not currently exist but I want to add them next year.

Screenshot 2026-09-22 at 18-52-06 boiler1.pdf.png caleffi_diagram.png Screenshot 2026-09-22 at 18-52-14 boiler2.pdf.png Screenshot 2026-09-22 at 18-52-18 boiler3.pdf.png Screenshot 2026-09-22 at 18-52-22 boiler4.pdf.png

Comments

  • hot_rod
    hot_rod Member Posts: 28,271

    The bottom drawing has the DirtMag upstream of the mix valve and circulator, I like that

    What calls the pump on ?

    One of the zones need to be open when the circ is running, or you want to add a bypass

    How does the smallest zone match the boiler output?

    it is a non modulating boiler you need to move the btus somewhere , into a load close to its output, or a buffer tank

    The ES boilers hold only 2,3 or 4 gallons of water on the 70, 105, or 140 sizes

    So it will hit setpoint quickly without a good load on it

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • kh7
    kh7 Member Posts: 3

    Indirect thermostat and single zone thermostat.
    Smallest zone is the DHW indirect right next to the boiler, doesn't short cycle on it.
    Only other zone is the single heating zone, but the boiler is oversized for sure 175/149mbh, ES2-6

  • hot_rod
    hot_rod Member Posts: 28,271

    Yikes, the mix valve will not tame that beast

    What us the load of the single zone?

    Keep in mind the calculated load is at a design condition. So on a mild day things look worse

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • kh7
    kh7 Member Posts: 3

    I'll have to wait until tomorrow to do the calculation but it's a 1,600 sqft house built in 1900 with 8 rooms/radiators, one of which is the size of a bus.

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