What units are used to measure the quantity of heat energy in a substance?

The measurement of heat energy in a substance can indeed be expressed in different units, with British thermal units (Btus) being one of the standard options. A British thermal unit is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. This unit is commonly used in the heating and cooling industries, making it particularly relevant in contexts involving thermal energy.

While Joules and calories are also valid units for measuring heat energy, their applications may vary based on context. Joules are the standard unit of energy in the International System of Units (SI) and can be used universally for various types of energy, including heat. Calories are specifically related to the amount of heat required to raise the temperature of water, similar to Btus, but are typically used in food energy contexts. Watts, on the other hand, measure power, which is the rate of energy transfer, rather than the total amount of energy.

Thus, British thermal units (Btus) are a prevalent choice for quantifying heat in specific applications, especially in the context of heating systems and energy efficiency analysis.