Single-stage and two-stage furnaces have operational differences.
Single-stage furnaces operate at only one output level – full capacity. This can lead to uneven heating and fluctuating bills because the temperature fluctuates more than with two-stage furnaces.
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.