On what basis are heat pump systems rated?

Heat pump systems are primarily rated based on their capacity to provide heating or cooling, which is commonly expressed in terms of tons. One ton is equivalent to the amount of heat required to melt one ton of ice in a 24-hour period, which is about 12,000 BTUs per hour. This measure indicates the system's ability to move heat and is a standard metric for comparing the performance of different heat pumps in both cooling and heating applications.

While BTUs per hour and other efficiency metrics like Energy Efficiency Ratio (EER) and Coefficient of Performance (COP) are important for understanding specific operational characteristics and efficiency, the tonnage rating provides a direct evaluation of the system's heating or cooling capability. Thus, the ton rating is widely recognized and used in the industry for determining the size and appropriateness of heat pump systems for specific applications.