What unit is used to measure the quantity of heat in a substance?

The British Thermal Unit (Btu) is a specific unit of measurement commonly used in the field of heating and air conditioning to quantify heat energy. One 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 makes it particularly relevant for HVAC applications, where heat transfer is a crucial factor in system design and efficiency.

While joules and calories are also valid units of heat measurement, the Btu is more widely utilized in the context of air conditioning and heating systems, especially in regions like the United States. The watt, on the other hand, is a unit of power, which reflects the rate of energy transfer rather than the quantity of heat itself. Understanding these differences helps in choosing the appropriate unit for specific applications in the heating and cooling industry.