Two-stage furnaces provide two different heating levels to keep a home comfortable regardless of its heating needs. On days when outside temperatures are moderate, the furnace operates at a lower level to provide efficient heating. This lower level also reduces the temperature differences residents experience with a traditional furnace. On colder days, the unit operates at the second level, providing the needed additional heat.
The lower heating level is sufficient in homes 80 percent of the time. However, on the coldest days of winter, it is unable to provide the heat to counteract the cold, so dual-stage furnaces use the second stage. When installing a single-stage furnace, HVAC professionals choose a unit operating at the second level all the time to ensure year-round comfort.
The dual-stage unit begins at its first stage, when the heat requirement is low. This eliminates the need to reach capacity immediately. The result is quieter operation without a sudden blast of air.
Low-speed operation improves filtration of the air in the home. The daily air exchange volume is increased. Home occupants find it easier to breathe with contaminates trapped by the filter.
Operating in the reduced level requires less fuel than standard furnaces. Ducts remain warm, reducing heat loss. In addition to the money saved, this reduces pollution.