What does BTU measure in heating and cooling systems?

The British Thermal Unit (BTU) is a unit of measurement used in the heating and cooling industry to quantify the amount of heat energy. Specifically, one BTU is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit at sea level. This foundational definition is critical in understanding how heating and cooling systems are rated and operated.

In the context of heating and cooling systems, BTUs are employed to express the energy output of various appliances, such as furnaces or air conditioners. For example, when sizing an air conditioning unit, the BTU rating helps determine how much heat the system can remove from a space per hour, which is vital for maintaining a comfortable indoor environment.

The other choices, while they relate to HVAC systems, do not accurately define what BTU measures. The total energy consumed in an hour pertain more to energy consumption metrics (like kilowatt-hours), while the total cooling capacity of an air conditioning unit typically involves the specific BTU rating but does not define BTU itself. Lastly, energy efficiency of an HVAC system is measured with different metrics such as SEER or EER, not BTU. This makes the correct answer particularly relevant to understanding HVAC specifications and performance.