A typical single stage furnace has one level of heat. If your furnace is 100,000 btu’s, each and every time the furnace starts and runs, the heating level is at the maximum (and only) setting. This is a very good thing on the coldest day of the year as you will need every one of those btu’s to heat your home.
In the Chicago area, the size of a furnace is based on being able to keep the home 70 degrees when the outside temperature is 10 below zero. However, it rarely gets that cold and the rest of the season your furnace is starting and stopping in short “cycles”.
Think of it as a car that can only go full speed or stop. It is great on the highway but not so good for driving the kids to school or running errands.
Running the furnace at full speed during most of the heating season (when it’s not ten below zero) causes shorter run times as the home heats up rather quickly given the furnace is running at its maximum (and only) heat level. This can cause major temperature swings and contribute to not only a potential higher energy bill, but a home that can be quite uncomfortable.
A two stage furnace is like having a large furnace for those subzero days when you really need it and a smaller furnace for the rest of the season when the temperatures are more typical of Chicago winters. The first stage level is set at 60% (or 60,000 btu in this example) and the second stage level is the maximum btu of the furnace (100,000 btu in this example).
According to ASHRAE (the American Society of Heating ,Refrigeration, and Air Conditioning Engineers) a typical two stage furnace in the Chicago area only uses the high (maximum) level of heat 17% of the time. That means that a single stage furnace is producing too much heat 83% of the time!
Producing too much heat not only costs money in energy usage it creates extreme temperature swings contributing to an uneven and uncomfortable environment.
A two stage furnace installed by a quality contractor will provide a more evenly heated and efficient living space. On the first stage (lower heat level) the blower motor is set to run at a slower speed which helps to reduce the “blast’ of heat associated with single stage furnaces. This provides a more gentle flow of heat throughout the home. If needed, you still have the second stage at the ready for those below zero days.
Operating the furnace on its first stage (lower heat level)has some additional benefits as well. If you are using a whole house humidifier, you can increase your overall comfort as the humidifier only operates when the heat is on. In a two stage furnace, the lower heat level coupled with the lower fan speed will keep the heat on a little longer allowing the humidifier to run for longer periods of time.
If you are using an electronic or media filter system, this longer, slower, cycle allows more circulation throughout the home filtering the air in your home more effectively.
Lastly, the technology used in a two stage furnace is simple and inexpensive. It is fairly commonplace and should not be considered a tricky “gadget” that can go bad and cost a fortune to repair.