A BTU is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.

• A. One degree Fahrenheit
• B. One degree Celsius
• C. One degree Kelvin
• D. One degree Rankine

Answer: (A)

A BTU is a unit of energy used in heating and cooling. It is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. This ties a specific amount of heat to a specific mass of water and a Fahrenheit temperature change, which is why Fahrenheit, not Celsius, Kelvin, or Rankine, is used in this definition. In practical terms, one BTU equals about 1055 joules, and HVAC calculations often express capacity in BTU per hour. The other temperature scales represent temperature, not the amount of energy needed to achieve a given temperature change, so they don’t define a BTU.