 The heat exchange surface areas and the corresponding temperature differential (between the refrigerant and the air stream) directly affect the operating pressures and hence the work the compressor has to do in order to provide the same heating or cooling effect.Generally, the larger the heat exchanger, the lower the temperature differential and the more efficient the system becomes.Heat exchangers are expensive, requiring drilling for some heat-pump types or large spaces to be efficient, and the heat pump industry generally competes on price rather than efficiency.