Which of the following units is used to measure heat energy?

The British Thermal Unit (BTU) is the correct unit used to measure heat energy, which is a crucial aspect in fields such as thermodynamics and HVAC (heating, ventilation, and air conditioning). A BTU is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit at a constant pressure. This unit is especially relevant in the context of heating and cooling systems, where understanding the amount of heat energy transferred is vital for assessing system efficiency and comfort levels.

For reference, while the Joule is also a unit of energy and can be used to express heat energy, it is a more universal measure of energy and is not specifically tailored to heat in the way that the BTU is. The Watt is a unit of power, which measures the rate at which energy is used or generated, rather than the energy itself. Lastly, Kelvin is a unit of temperature measurement rather than energy, and it indicates the absolute temperature scale, which is important in thermal dynamics but does not measure heat energy directly. Therefore, BTU stands out as the specialized unit pertinent to measuring heat energy in practical applications.