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I'm buying a 4 bedroom 1200 SF 1.5 story house and the seller is installing a 100K BTU boiler with a 96% efficiency rating. Is this enough for this size of house in Chicago?


  • John Starcher_4
    John Starcher_4 Member Posts: 794
    The answer is..............


    This question cannot be answered strictly based on square footage alone, nor can any question regarding the proper size heating unit for a structure. You need to have a full heat-loss analysis performed for the home, and preferably one that includes a blower door test to determine the amount of air infiltration.

    Most reputable heating contractors can perform this service, although I would expect a fee will be charged for doing so - it can get to be a bit time consuming to do it properly.

    [email protected] Member Posts: 9
    100 mbh

  • jim lockard
    jim lockard Member Posts: 1,059
    need more info

    like area of North facing lake front window wall or drafty old doors ? The point is James without a heat loss cal. you will not know.Best Wishes J.Lockard
  • Jed_2
    Jed_2 Member Posts: 781

    A house can be sized based on sq ft alone. Done it many times WITHOUT call backs. But, something needs to be known about the house construction. Worst case realistic SWAG is 65,000 btu/h, unless it's rough sawn barnboard, lathe&plaster, or brick and no sheathing either side, or a pole barn.

  • hr
    hr Member Posts: 6,106
    It could be grossly oversized !

    a heat loss calc is the only way to get a real close answer. Many new construction homes these days fall in the 17-20 BTU/sq. ft. range.

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  • Weezbo
    Weezbo Member Posts: 6,232
    some heat load idea would be good :)

    you may have tight construction,in such a case maybe you might only need 1/2 of that ability it maybe older leaky poorly insulated badly designed field distribution layout ,PP zoning etc. in which case boiler size is of nearly no concequence because unless the ditribution system is On the mark as it were the boiler it self isnt going to Do it for you in some corner of the home.
  • Ken_8
    Ken_8 Member Posts: 1,640
    Hot Rod's right!

    However, a free heat load calculator is available for your own use if you go to the top left of this website and check out the list of items on the little pipe plate, you'll see a topic that says, "Free Heat Loss Calcs," (5th from the bottom).

    That little program allows you to find out EXACTLY how many BTU's you need to heat the house in any town on earth.

    Any problems? Any one of us could help.

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  • Constantin
    Constantin Member Posts: 3,782
    Go for Heat Loss Calculation

    There are a number of free heat-loss calculators available. I would use one to figure out what is actually needed, particularly if you're considering retrofitting the structure with insulation. Another consideration is the radiators in place, if they're steam-based, your heating plant will need more oomph to get them going than many small (and otherwise correctly-sized) boilers can provide.

    So, instead of having the seller install a boiler that may or may not meet your needs. I'd get one of the better heat-loss/heat gain programs, figure out heat losses, and then decide what does and what does not need updating. You have a whole summer to figure it out... and you'll benefit from your decisions over the long run.

    To give you some perspective, the heating plant in our home will have an 116kBTU IBR output rating... for a 5,000 sq ft house in a cold climate. However, we're taking our house to new hights re: insulation. A brick house with no insulation can be very "lossy" indeed!

    Lastly, do not discount using alternate fuels. For example, in the Boston market, oil is about 40% cheaper than city gas and 50% less than propane. This may or may not hold true for your market... however, it is worth looking into. Initially, I was sold on a modulating, condensing gas boiler myself... then I saw the cost difference between the pinnacle of gas technology and a simple oil-system (on-off, non-condensing). For us, it makes sense to stick with oil, but YMMV, of course, and fuel prices vary quite a bit geographically.
  • Boilerpro_3
    Boilerpro_3 Member Posts: 1,231
    No call backs, just big fuel bills and shorter life.

    FYI 65,000 btu/hr would comfortably heat my 1906 2800 sq ft two story frame with 700 sq ft of windows here in Northern Illinois down to about -15 below on a windy day. Design temp here is about -4. A 100,000 btu/hr boiler is probably twice as big as needed for 1200 sq ft, but heat load calcs must be done to be sure. Sweet home Chicago is just 2 hour due east of me and design requirements are about the same.

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