What is BTU?

It doesn't matter where you live and what measurement system you use, if you start looking for a wood or any other kind of a stove online, you'll see that the heat output can be in BTUs and chances are it may get you baffled.

The BTU, or British thermal unit, is the unit of Imperial system for measuring energy and mainly used only in the United States. It's 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 BTU is defined as 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 in different conversions fluctuates in no more than 0.5%.

Some more conversions:

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

As you now know what the BTU is, you shouldn't feel lost in the vast ocean of stoves, fireplaces, burners, and furnaces.

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