So let’s first begin by defining what a two-stage furnace is. When you see the term “stage”, what they are really referring to is the burner mechanism within your furnace. More specifically, the reference is to the valve that controls the flow of fuel to the burner itself. On old fashioned, one-stage furnaces, this value had two positions: opened or closed. With newer two-stage furnaces, this valve now has three distinct positions: fully opened, partially opened, and closed. Having this third position allows the furnace to either operate at full-blast capacity (just like other furnaces) or at a reduced output where it uses less fuel and provides about 60-65% of the heating of the full blast mode. If after a few minutes the furnace has not met the heating demands of the thermostat, the furnace will kick into full blast mode at that time and complete the job.
There are three primary benefits to utilizing a two-stage furnace. The most obvious and tangible benefit is that it should result in a reduction in your monthly energy costs. On days when it is only moderately cold outside, instead of running in full blast mode and wasting energy, the furnace will instead automatically run in partially open mode. This will minimize the amount of energy expended by the furnace and ultimately will reduce your monthly energy bill.
The second benefit is less obvious. The two-stage furnace will do a better job of evenly heating your house and removing cold spots. A one stage furnace will quickly heat your house and then turn off quicker, making temperature fluctuations more pronounced and allowing cold spots to re-emerge. Because the two-stage furnace produces less overall heat in partially open mode, it will run more consistently, allowing the heat to circulate more evenly in your house.
The final benefit is also less obvious, in that the two-stage furnace will provide better filtering for the air in your house. This is because, by its nature, the two-stage furnace will run more often. And because it is running more often, that means it is pushing more air through your house’s duct work, and more circulating air leads to better air filtration. Keep in mind that a two-stage furnace will cost you more money up front, but should pay for itself in the long run with savings it gathers from your energy bill. Ultimately the decision as to whether a two-stage furnace is a worthwhile investment will come down to your personal needs.