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Minimum Oil Fired Hot Water Boiler Water Temperature in Summer to Prevent Condensation

BrooklynMike
BrooklynMike Member Posts: 39
in Oil Heating

I have a Weil McClain WGTO4 boiler with tankless coil that feeds a 40 gallon Electric Hot Water heater with mixing valve on the output. Have connected an elapsed time meter to the 240VAC to the water heater and the tank turns on very infrequently due to the high water temperature going into the tank and the mixing valve reducing flow from the tank. During the non- heating season, what is the minimum aquastat setting to prevent condensation in the boiler. Also, I seen posts that warn against condensation forming in a cold boiler( shut down) when running cold water through the tankless coil. I have a heavy duty dehumidifier running in the basement near the boiler and think this may eliminate the condensation concern.

Comments

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 17,816

    Does the boiler maintain water temp with an aquastat? Or does a stat in the EWH fire the boiler.

    If the aqustat is running the boiler you shouldn't have an issue @135 but you may need it hotter than that to prevent the EWH elements from coming on.

    Even if the sensor in the tank fires the boiler it depends how long it take for the return to the boiler to come up to 130. 15 min is ok.

  • BrooklynMike
    BrooklynMike Member Posts: 39

    Ed,

    Thanks. The aquastat controls the boiler water temp. I am thinking about this for the non- heating season when there is no return flow. Assuming a 10 degree differential in the aquastat, I would set it at 145 so the burner fires at 135 degrees.

  • HVACNUT
    HVACNUT Member Posts: 6,773
    edited April 26

    You're confused. During the burner run time, the flue temperature should exceed the dew point, which is 135°. There should be no problem with that when recovering from a 10° or higher differential. If you want to turn the Low as low as it goes and rely solely on the electric, that's fine. And since the mandate of ULSD, the cast iron is safer than it was concerning low flue gas temperatures.

    If you still want to use the boiler to heat the water in summer, set the Low 20° above the required mix temperature. If the mix is set to 120°, set the low to 140° with a 10° differential.

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