What’s the Difference Between a Single Stage, 2-Stage & Variable Speed Furnace?
Choosing the right furnace for your home begins with evaluating several factors including heating requirements, existing ductwork and insulation, the size of your home and the number of levels, and, of course, your budget. Armed with that information, your HVAC professional can help you determine which type will best meet your needs: single stage furnace, 2-stage furnace or variable speed furnace.
Here is an overview of these three types:
1. Single-Stage Furnace
The single-stage furnace, also called a one-stage furnace, operates with only two settings: “on” or “off.” When it is on, it is at the maximum level of heat output, with no adjustment for how warm or cold it is outside or within different areas of your home. Because this type of furnace is always on “high,” it lags in energy efficiency behind the other options.
2. Two-Stage Furnace
The two-stage furnace is a step up in efficiency from the single-stage furnace, with two stages that allow for some adjustment for changes in temperature. Most (about 75%) of the time, this type of furnace operates in the first stage which is approximately 65-75% of the furnace’s capacity, saving on energy. When the temperature drops and more heat is needed, the second stage engages to meet the current heating requirements for as long as necessary. Once the temperature warms up again, operation returns to normal, so you are only paying for the additional energy when you need it. Because of the lower output most of the time, the furnace does run longer, but this also allows for more even heat distribution.Two-stage furnaces have quieter operation, are more efficient and are better for the environment.
3. Variable Speed Furnace
The variable speed furnace offers the most flexibility in terms of operation and energy use. Instead of stages, this furnace relies on a fan motor operating at different speeds to adjust the amount of heat output produced. Increased airflow results in greater comfort, because temperature is more consistent throughout the home, and better air quality because more air goes through the filter. Even when the furnace is not heating, air can continue to circulate, which actually reduces the need for it to turn on as often. This results in energy savings and lower utility bills. An added bonus: the variable speed furnace is quieter than the single-stage or two-stage furnaces.
Rheem manufactures all three types of furnace.