Single-stage and two-stage furnaces differ in their heating output capabilities:
Single-stage furnaces have only one setting, they either operate at 100% or are off. This may cause temperature fluctuations and higher energy bills because the furnace is either running at its maximum setting or completely off..
Two-stage furnaces can run at both low and high speed. This allows the furnace to modulate its output based on the actual heating demand, resulting in more consistent temperatures, quieter operation, and improved energy efficiency. A two-stage furnace may be a more expensive initial investment, but it can provide greater comfort and savings over time.