Design cooling load is the amount of cooling energy required to maintain a comfortable indoor environment in a given space. It is determined by the size of the space, the amount of insulation, the number of windows, the type of construction, and the climate. The cooling load is typically expressed in British Thermal Units (BTUs) per hour. It is important to accurately calculate the design cooling load in order to select the right size of HVAC system for the space. An undersized system will not be able to adequately cool the space, while an oversized system will be inefficient and costly to operate.