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Replacing old oil boiler

george_42 Member Posts: 121
I have an older oil fired boiler with baseboard heat and we are converting to gas. My concern is that a modern modcon boiler will not give me the higher temperatures (180 degrees ) that I need  for the baseboard to heat the house . I think that I will have to use a traditional gas boiler . Any thoughts .


  • icesailor
    icesailor Member Posts: 7,265
    Baseboard Temperatures:

    Do an accurate heat loss calculation on the building and compare that to the installed radiation. You will probably find that the building is severely over radiated and doesn't need 180 degree water.

    If on the coldest days of the year, the heating system maintained inside temperature, and you ever heard the circulator stop, the house is over radiated.

  • furnacefigher15
    furnacefigher15 Member Posts: 514
    Mod cons

    A mod con can and will provide 180 degree water. The issue is that while it is doing so it will no be running at peak efficiency.

    The baseboard only needs to be 180 at design conditions (coldest weather)

    The rest of the time the water temps can be lower and most of the time much lower.

    Depending on the climate in the area you live, you may only need 180 degrees a few days of the year.

    I know here in Chicago that most of the winter and shoulder heating months are fairly mild usually in the 30 to 50 degree range.

    So most of the heating season, the water temps only need to be in the 120 to 150 degree range.

    When you have the heat loss done, do at design to find the boiler size requirement, and also do it at 20, 40 and 50 degree outdoor temps, and that will give you an idea of what the load is during the shoulder months, and with that you can find the needed water temps at those outdoor temperatures.
  • meplumber
    meplumber Member Posts: 678
    edited April 2012
    I agree to a point....

    Follow the above advice.  It is spot on.

    To FurnaceFighter, most of the Mod/Cons from Europe are limited to 174 deg F.  That number is not adjustable.  Viessmann Vitodens 200 is limited to 167.  As you stated, the biggest drawback is that the mod/con is not very efficient at higher operating temps. 

    I have had two residential and a handful of commercial projects recently where bid-spec buildings were built with exactly the amount of high temp radiation needed at design condition.

    On one of these jobs, the contractor that did the change out used a Vitodens 200 (which is my favorite mod/con, hands down).  The customer complained of not making setpoint in the dead of winter.  We made some minor adjustments and made the system constant circ and that helped a lot.  We added additional radiation the following summer.

    These were extreme cases, but highlights the need to have a proper heat loss done and compare that with the actual radiation in place.

    Good Luck
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