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Just Curious

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Gene_7
Gene_7 Member Posts: 10
in THE MAIN WALL
Is there a formula to figure out how many more BTU's you would need produce, if the temp was 7% colder than the previous day? Thanks.

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  • Jamie Hall
    Jamie Hall Member Posts: 23,321
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    Not from that

    information alone.  You would need to know, also, the two temperatures (7% colder is not a really useful number -- based on what temperature scale?  Relative to what?  Starting where?) outside, and the temperature you were maintaining inside.  Then you could get the ratio of heat losses, all else being equal -- and from that you could obtain the additional BTUs, provided you knew the BTU load on one day or the other.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Gene_7
    Gene_7 Member Posts: 10
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    More Information

    OK, here is the scenario: 1000 Sq Ft Home at 70 Degrees Fahrenheit inside. Outside temp is 32.3 Degrees Fahrenheit. The next day is 30 Degrees Fahrenheit (a temperature drop of about 7%). How many more BTU's are required on Day 2 to maintain the 70 Degree Farhenheit inside? What would be the formula to figure this? 
  • Gene_7
    Gene_7 Member Posts: 10
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    More More Information

    Sorry, I missed that the BTU load on Day One was 42000. Please keep in mind this is all hypothetical. Thanks again.
  • CMadatMe
    CMadatMe Member Posts: 3,086
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    Simple

    You did a heat loss correct? Just change the outdoor temp to your day temp. You could basically graph yourself your own chart.

    There was an error rendering this rich post.

  • Jamie Hall
    Jamie Hall Member Posts: 23,321
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    OK, now it's easy

    Heat flow (power) is equal to the difference in temperature times the thermal conductance times the area.  Energy (BTUh) is equal to power times time.  So lumping a whole bunch of constants together as one, one can solve that and say that a constant -- we'll call it K! -- is equal to energy divided by the difference in temperature.  In this case, 42,000 divided by 37.7, or 1110.  Now to get the energy required for any other difference in temperature, just multiply the constant time the difference in temperature -- for the second day, 1110*40, or 44,600.



    The constant will be constant -- assuming all else equal, and a whole bunch of other things, and works only if the temperature inside and outside on both days was also constant (it is not exactly valid for an average temperature, except under some rather special mathematical constraints).



    This, incidentally, is how your friendly fuel company, if you have oil and are on automatic delivery, works out when to come and feed your tank.



    That what you were after?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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