The answer to 'single stage vs two stage furnace' is that a two-stage furnace is generally more energy-efficient and provides better temperature control compared to a single-stage furnace. A two-stage furnace has two levels of heating output - high and low - which allows it to better match the heating needs of your home. This results in more consistent temperatures, reduced temperature swings, and lower energy bills. Single-stage furnaces only have one heating level, so they tend to cycle on and off more frequently to maintain the desired temperature.
Two-stage furnaces are also quieter and provide better humidity control. However, they do cost more upfront than single-stage models. The best choice depends on your home's size, insulation, climate, and your budget and energy-efficiency goals.