Single stage furnaces are available with 80% and 95% efficiencies. They are typically the most economically priced furnaces. With this type of furnace, there is only one “speed” or stage. To explain this type of furnace simply, think of your car and gas pedal. When this type of furnace starts, it is like having the gas pedal to the floor immediately. It can also be said that it’s “all on” or “all off”. So the same amount of gas and electricity are used every time it runs.
It is also harder to control consistent temperatures and humidity levels with a single stage furnace. While a single stage furnace will certainly do the job in heating your home, you will probably not achieve the comfort levels you would get with a modulating or two-stage, variable speed furnace.