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Heat anticipater question.

nibs Member Posts: 516
Looking for the short answer.
My good Honey of a mercury thermostat is allowing a 2.5deg F drop from boiler shut down to re lighting.
Should we make the boiler cycle longer or shorter. Thin slab radiant with lots of thermal mass.
The boiler usually starts once a day in late evening, (2 or 3 am if we light a fire) and runs until noon or 2 pm depending on outside temp. If it is below 10F and not sunny it will likely stay on 24 hrs. Would like to get the range down in the 1 or 1.5 deg area. Have watched vids on how to adjust the thermostat but since the boiler is not cycling very often, cannot seem to get this rusty ole head around which way to move the anticipator lever. It was set a 3 and now have it at 2.5,
My good multimeter was swiped along with my red toolbox and have yet to replace, so am looking for the trial and error solution,
Thanks, Tony.


  • ch4man
    ch4man Member Posts: 296
    the anticipator scale will also have an arrow and the word "longer" on it. i forget which way the number scale goes with the arrow but " longer" means longer run times= more overshoot and greater cut in/ cut out differential
    so dont set it any longer.
    heat anticipators add false heat during the on cycle to cycle the burner off a bit before set temperature is reached, it anticipates the residual heat in a large mass heat-x (forced air) that can continue to heat the space even after the burner is off
  • Zman
    Zman Member Posts: 7,606
    Just adjusting an anticipator will not solve overshoot in a high mass system. Outdoor reset and indoor feedback is the best way.
    Outdoor reset and PWM algorithm t-stats will help considerably. https://www.supplyhouse.com/Uponor-Wirsbo-A3100101-Heat-only-Thermostat-with-Touchscreen?gclid=Cj0KCQiAm4TyBRDgARIsAOU75sqJGXHAlV1DV7Hz0oiMocEE5Rp8li_G5RV7c_TVo-OMKrtbh632uXwaAjClEALw_wcB
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    HVACNUT Member Posts: 5,888
    @Jamie Hall
    You've mentioned the venerable T87 thermostat many times, so I'll consider you the resident expert.

    As far as I know, the heat anticipator should be set to the sum, in amps, of all the controls in its circuit. Gas valve, switching relay, zone valve, etc. The greater the amp draw, the longer the cycle?

    Can the anticipator be used as a CPH control?
  • Jamie Hall
    Jamie Hall Member Posts: 23,650
    Understanding is correct, the @HVACNUT ! But that's really a starting point. If one is fussy, one can always move it a bit one way or the other to get more comfortable.

    It's not really a cycle per hour control, although it sort of does that -- the cycle length resulting will depend on how fast the building loses heat.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • nibs
    nibs Member Posts: 516
    Thanks all, we have no overshoot problem, because the house responds so slowly, the max temp we reach is happy time, would just like to even out the temp a little more. The ODR modulates the boiler beautifully, and after the boiler has been running for a while delta T is often less than 10 deg at manifolds.
    Will try shortening the run time. Most of the instructions online are directed towards furnace cycling so do not really come close to our situation.
    Thanks to all the help we got here while building the system we are very happy with the results, now down to the fine adjusts.
  • nicholas bonham-carter
    Maybe the ODR should be evening out this loop. Is there a floor sensor on it. Maybe the thermostat and ODR are each fighting for control.—NBC