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Heat Loss

James Day_2
James Day_2 Member Posts: 191
Hey guys,

   I am looking at a boiler replacement job.  The current boiler is 220,000 btu.(Oil).  It is zoned with zone valves and has an indirect hot water tank.  The house is 4700 sqft.  Has most of the old single pane w/storm windows.  Customer insulated all outside walls a few years ago with blown in insulation.   I did a heat loss using my program and it comes up with 95,000 btu heat loss.  This seems a little light to me.  Do you think my calculations could be correct for such a large house?  Thanks,  James


  • icesailor
    icesailor Member Posts: 7,265
    Heat Loss:

    No, that doesn't sound high to me. In fact, it sounds high. If you did an accurate heat loss, and you covered your bases, I think you will be OK. Some others may not agree but I have never had a problem with those kind of numbers. But I haven't seen the house.

    If you are comfortable with your numbers, run it back and leave out the insulation. You will be surprised at how much more radiation you need and a larger boiler.
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,314
    Depends on where the house is

    the region dictates the boiler needed. Long Island needs a smaller boiler than northern Vermont.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • Trust your numbers

    I'd double check them and maybe have one of your suppliers check your numbers, but 20 BTU's per square foot doesn't sound too far off.

    I think you will be covered, especially on a zoned system.  Typically, all the zones will not call for heat at the same time.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • James Day_2
    James Day_2 Member Posts: 191
    pick up factor

    would you add any pick up to that number, or would you size the boiler exact to my heat loss?
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Reality Scares

    I agree with the rest of the guys. Sounds ok for a climate using 0 degrees as a design temp. If your not accustomed to doing heat losses past install comparisions take over the thinking. Trust in the numbers. I get contractors telling me all the time I am crazy if I think that house will be comfortable based on the losses I provide them.  Generally 3,000 sqft home is between 36 and 50K depending on the construction based on my experience. Never been bitten in over 20 years doing them.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • icesailor
    icesailor Member Posts: 7,265
    Heat Loss:

    Same here in over 35 years.
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    same here

    but I am concerned about single pane windows. that basically doubles your window load and you should consider the impact on infiltration as well.

    as long as you are treating those two things appropriately, I'd go ahead. 20 BTU/sq ft average for a big home is a very high load.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
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