A British Thermal Unit, or BTU, is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. In the International System of Units (SI), commonly known as metric, heat is expressed not in BTUs, but in Joules. One Joule is defined as the amount of energy required to accelerate a mass of one kilogram at a rate of one meter per second squared, over a distance of one meter. The two are related by a factor of about a thousand:
1 BTU is 1,055.06 Joules (J), or slightly more than 1 kilojoule (kJ)
Why are we bothering with this? Because these terms are important when comparing the relative powers of heat sources that brewers use to boil water and wort:
- Kitchen stoves
- Propane burners
- Natural gas burners
- Electric heating elements