British Thermal Unit - Definitions

Definitions

A Btu is defined as amount of heat required to raise the temperature of one 1 pound (0.454 kg) of liquid water by 1 °F (0.556 °C) at a constant pressure of one atmosphere. As is the case with the calorie, several different definitions of the Btu exist, which are based on different water temperatures and therefore vary by up to 0.5%: A Btu can be approximated as the heat produced by burning a single wooden match or as the amount of energy it would take to lift a one-pound weight to a height of 778 feet (237 m).

Nominal temperature Btu equivalent in joules Notes
39 °F (3.9 °C) ≈ 1059.67 Uses the calorie value of water at its maximum density (4 °C or 39.2 °F)
Mean ≈ 1055.87 Uses a calorie averaged over water temperatures 0 to 100 °C (32 to 212 °F)
IT ≡ 1055.05585262 The most widespread Btu, uses the International Table (IT) calorie, which was defined by the Fifth International Conference on the Properties of Steam (London, July 1956) to be exactly 4.1868 J
ISO ≡ 1055.056 International standard ISO 31-4 on Quantities and units—Part 4: Heat, Appendix A. This value uses the IT calorie and is rounded to a realistic accuracy
59 °F (15.0 °C) ≡ 1054.804 Chiefly American. Uses the 15 °C calorie, itself now defined as exactly 4.1855 J (Comité international 1950; PV, 1950, 22, 79–80)
60 °F (15.6 °C) ≈ 1054.68 Chiefly Canadian
63 °F (17.2 °C) ≈ 1054.6
Thermochemical ≡ 1054.35026444 Uses the "thermochemical calorie" of exactly 4.184 J

Read more about this topic:  British Thermal Unit

Famous quotes containing the word definitions:

    What I do not like about our definitions of genius is that there is in them nothing of the day of judgment, nothing of resounding through eternity and nothing of the footsteps of the Almighty.
    —G.C. (Georg Christoph)

    The loosening, for some people, of rigid role definitions for men and women has shown that dads can be great at calming babies—if they take the time and make the effort to learn how. It’s that time and effort that not only teaches the dad how to calm the babies, but also turns him into a parent, just as the time and effort the mother puts into the babies turns her into a parent.
    Pamela Patrick Novotny (20th century)

    Lord Byron is an exceedingly interesting person, and as such is it not to be regretted that he is a slave to the vilest and most vulgar prejudices, and as mad as the winds?
    There have been many definitions of beauty in art. What is it? Beauty is what the untrained eyes consider abominable.
    Edmond De Goncourt (1822–1896)