Which of the following best describes how many degrees a BTU will change when measuring water?

The best description of how many degrees a BTU will change when measuring water is one pound. A BTU, which stands for British Thermal Unit, is defined as the amount of energy required to raise the temperature of one pound of water by one degree Fahrenheit at a constant pressure. This is a fundamental concept in thermodynamics and is crucial for understanding heating and cooling processes involving water in HVAC applications.

Water has a specific heat capacity of about 1 BTU/(lb·°F), making it essential in various heating and cooling calculations. Therefore, knowing that a BTU will change the temperature of one pound of water by one degree is vital for HVAC professionals who need to calculate energy needs and efficiencies in their systems.

The other options do not align with this definition, as a gallon is a volume measurement, a liter is also a volume measurement (approximately 2.2 pounds of water), and a cubic foot is also a measure of volume that varies with density and does not directly relate to temperature change in the same straightforward manner as weight does with water.