What is BTU?

When you're looking for a new stove, fireplace, or air-conditioning device, a question "what is BTU" can strike you all of a sudden. In most cases it doesn't matter where you live and what measurement system you use, if you start looking for hearth or cooling products online or even in a real life, you'll see that the heat output or cooling capacity can be in BTUs and chances are it may get you baffled.

So, what is BTU after all? The BTU stands for British thermal unit and it is the unit of Imperial system for measuring energy. It is mainly used in English speaking countries, such as United States, Great Britain, Canada, and New Zealand, but can be used also in any country around the world. The BTU is used for measuring heat output of heating devices as well as energy output of other equipment in the power, steam, and air conditioning industries. It may be used as a unit of power, but in the form of BTU/h, BTU per hour; quite often though the "per hour" part is dropped and people treat it just as BTU.

The scientific definition of BTU is the amount of heat required to raise temperature of one pound of water by one degree Fahrenheit. Its metric counterpart is the Joule, and it converts as 1 BTU = 1055.56 Joules by the ISO standards. There is no absolute conversion though as it involves calories, but variance for different conversions fluctuates in no more than 0.5%. A prefix M can be added for thousands BTUs – MBTU – and for millions, a double M is added – MMBTU. Hundred thousand BTUs is equal to one therm and if you're keen on really big numbers, you should like this one: quad – is one quadrillion BTU (that's one and fifteen zeros).

And to make you completely prepared for the time when the question "What is BTU" comes, some more conversions for you:

1 BTU » 252 cal » 0.252 kcal 1000 BTU/h » 293 W

1 W » 3.41 BTU/h 1 Hp (horsepower) » 2,544 BTU/h

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