Heat - Measurement Units

The measurement unit for heat in the English system is British Thermal Unit (BTU). A BTU is defined as the amount of heat required to raise the temperature of one pound of water by 1 degree Fahrenheit (F).

For example, consider a medium sized water bottle in your refrigerator. It should have about a pound of water in it. In the refrigerator, the water temperature is about 40 deg F. If you take the water bottle out of the refrigerator and put it on a kitchen shelf, its temperature will start to rise. Within a minute or so, its temperature will be 41 deg F. The water just absorbed 1 BTU from the ambient air. This should give you an idea about the magnitude of a BTU.

The figure provided here illustrates the magnitude of 1 BTU. In this figure we are showing one pound of water in a beaker. To heat this water, we turn the flame on and its temperature rises by one degree Fahrenheit.