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Oil to NG Conversion

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BostonGTR
BostonGTR Member Posts: 18
in Gas Heating
I’m converting from oil to NG.  13 yr old house with good insulation, windows and doors with 3 hydro-air units.  Given that the hydro-air units have aquastats set at 140 degrees; what is the best boiler solution?  Am I correct that a modcon unit will not be

in the “sweet spot” i.e. not condensing, due to the need to generate approximately 170 degree water for the air handlers; not to mention the need to generate hot water for an indirect DHW tank?  Even if the modcon is not condensing and therefore not operating at 96% efficiency; will it still be more efficient, or at least as efficient, as a new cast iron boiler?  I understand that the modcon would require some annual maintenance.  Is the cast iron boiler maintenance free?  The 96% modcon unit offers a rebate of $1,500; the rebate drops to $1,000 for a rating of 90%+; and then to $0 below 90%.  Might you be able to recommend a “medium efficient” cast iron boiler with a 90% rating? 

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  • SWEI
    SWEI Member Posts: 7,356
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    rest of system

    Are other emitters (radiators, floor tubing, etc) involved, or just the hydro-air units?
  • BostonGTR
    BostonGTR Member Posts: 18
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    Only Hydro-Air

    Just the 3 hydro-air units.  
  • SWEI
    SWEI Member Posts: 7,356
    edited October 2012
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    outdoor reset

    Works on air coils too.  The curve will be higher and steeper, but it will noticeably improve comfort and efficiency.  Depending on the coil sizing and the climate, a mod/con could be condensing more of the time than you'd expect.



    Edit: looks like the aquastat controls the fan, so making ODR work properly would require some additional controls.
  • BostonGTR
    BostonGTR Member Posts: 18
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    Feedback

    Does anyone have any experience using a modcon boiler to feed a hydro-air system? It seems that it shouldn't perform any worse than a cast iron unit; correct?  I just want to make the correct boiler decision (modcon vs. cast iron) before proceeding with this heart transplant.
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