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outside air reset ouestion

Joe Brix
Joe Brix Member Posts: 626
I need 170° in the baeboards when it's in the teens but 150° is fine for most of the winter with 135° return. Of course, the 260 drives the boiler to 170° when the indirect calls. I don't see any issues with 130° water return on an oil boiler. While the temp reset is not drastic, I think the unit should easily pay for itself in 2 seasons with #2 oil in the average of over $2.30/gal.

I also notice less expansion noise in the Baseboard and more even heating.


  • freyheating265342
    freyheating265342 Member Posts: 14
    outside air reset

    i understand that using outside air reset controlers saves fuel by lowering the boiler water temp. typical aquastat settings are 180/160, now if out side air temp is telling the boiler to make lower temp heating water, lets say 150* or 160*, that means our return water temp is not at a safe temp for a typical cast iron boiler. were is the savings if the boiler craps out early. i`m a firm believer in the KISS mentality.
  • Brad White_9
    Brad White_9 Member Posts: 2,440
    Properly done

    Outdoor reset on a CI boiler involves a 4-way or a 3-way mixing valve or injection valve or circulator. Either of these, as part of their regulatory functions also serve to elevate the HWR temperature should it fall to the danger zone (130-140 F return to the boiler.)

    True, your boiler reset is limited with cast iron boilers, as you said from 180 to 150 or so supply water temperature. That is only part of the savings.

    The real savings is when the radiation side is decoupled from the (protected) boiler. The independent radiation loop "sips" hot water from the boiler loop and can enjoy deep setbacks from a high of full boiler temperature to a low of practically just above room temperature. Within that the boiler throughput is limited (low radiation temperature means fractional boiler draw).

    Sure, if you destroy your boiler through misapplication there is no savings. The solution? Like the doctor said to the patient, "don't do that".
  • hydronicsmike
    hydronicsmike Member Posts: 855


    Outdoor Reset does improve the overall system efficiency geatly and minimizes temperature sswings and expansion noises.

    As mentioned above, for boiler protection, a mixing device should be used.

    Have a look at tekmar tN4. It is a completely communicating system that even without mixing could provide flue gas condensation protection by being able to shut off zones. However, it could not do thermal shock protection without a mixing device in between the boiler loop and the zones.

    If you like to discuss, call tekmar at 250-545-6649...

  • Mad Dog_2
    Mad Dog_2 Member Posts: 6,720
    Any run-of-the-mill Cast Iron boiler can be piped

    to accomodate those low temps without flue gas condensation. P/S. Out Mad Dog

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  • Mad Dog_2
    Mad Dog_2 Member Posts: 6,720
    Yeah Joe......................................

    AND IF the radiation is a bit oversized as we see in many homes.....we can have a peak temp of 150 or lower. Mad Dog

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This discussion has been closed.