"Two-stage cooling means the air conditioner (or heat pump product) has a compressor with two levels of operation: high for hot summer days and low for milder days. Since the low setting is adequate to meet household cooling demands 80% of the time, a two-stage unit runs for longer periods and produces more even temperatures. Longer cooling cycles also translate to quieter, more efficient operation and enhanced humidity control. Compared to a single stage unit, a two stage air conditioner (or heat pump) can remove twice as much moisture from the air. This is important because when moisture levels are high, there's a higher potential for mold and other pollutant problems."