How many calories are approximately equal to 1 BTU?

The correct answer is 252 because one British Thermal Unit (BTU) is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. In the context of energy conversion, 1 BTU is approximately equal to 252 calories. This is a standard conversion used in thermodynamics, particularly when dealing with heat exchange and energy transfer, making it a useful figure in various applications, including HVAC and energy calculations.

The other choices represent figures that do not accurately reflect the energy equivalence of BTUs in relation to calories. Understanding the relationship between different units of heat measurement is essential for machinist mates, as it aids in understanding heating systems and processes they may encounter.