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Temperature Overshoot

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qwerty
qwerty Member Posts: 3
I'm having a problem with temperature overshoot. I had 12 cast iron radiators on one thermostat. I cut out all the 2 inch cast iron pipe in basement and ran 1 inch pex. Now I have 3 rads on each thermostat. I put thermostat on 70 and circulators turn off at 70 but rads get so hot that temp rises to 74 degrees. Also had whole house insulated.

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  • Zman
    Zman Member Posts: 7,605
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    What type of boiler do you have?
    Outdoor reset would fix this.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    Solid_Fuel_Man
  • qwerty
    qwerty Member Posts: 3
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    I have a crown gas boiler with a tankless coil.
  • Jamie Hall
    Jamie Hall Member Posts: 23,635
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    What kind of thermostat are you running? Many "old fashioned" thermostats had what was called an anticipator -- which could be easily adjusted to fix that problem. Took a little fiddling and some patience -- a couple of days of trial and error -- but quite easily done.

    Some newer digital thermostats are alleged to be able to "learn" about the overshoot, and some of them seem to be able to do that pretty well -- but not recovering from a setback.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
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    Outdoor reset.....or at least run the boiler at a much lower temperature. 

    That tankless coil is wasting so much fuel you would throw up if you knew. Indirect or a stand alone electric/heat pump water heater is the way to go. 
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • qwerty
    qwerty Member Posts: 3
    edited November 2020
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    I will probably do an outdoor reset in the near future and get rid of the tankless coil. I have a Honeywell RTH2300 digital thermostat that has an advanced setting like a heat anticipator. The numbers are 2 for steam, 3 for hot water, 5 for a furnace and 6 for electric. Which setting would make the heat turn off the soonest?
  • Jamie Hall
    Jamie Hall Member Posts: 23,635
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    2 is what you want for a radiant floor.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
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    Try it at 1. The lower the better. If you find the temperature swings are too much at 1 then try 2. 
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!