The More Stages, The Better

The More Stages, The Better

Modulating, Single Stage & Two Stage Furnaces

By  |  Product Expert
By  |  Product Expert

Two-stage furnaceAre you considering replacing your furnace but are confused by terms like “single-stage,” “two-stage,” and “modulating?”

If your furnace is more than 10-15 years old, chances are that it is a single-stage unit with an efficiency rating of less than 80%. Upgrading to a higher efficiency model now can save you a lot of money in the long run and you'll be surprised to see that it only takes a couple years to recoup the initial costs, putting money back in your pocket in no time!

So, let's take a look at “staging” and how it impacts your comfort and your wallet.



Staging is a unit's ability to operate at various stages of performance. Furnaces are rated in three distinct categories of staging: Single-Stage, Two-Stage, and Modulating.

Single-Stage: These units operate in one way: On or Off. If your system needs the furnace, it kicks on at 100% power until the demand is met and then shuts off completely. Essentially, it’s like having two speeds in your car, 0 MPH and 100 MPH.

Two-Stage: Furnaces rated as Two-Stage offer increased flexibility, with two set operating conditions, allowing for an in-between setting when demand isn’t very high. The car equivalent of a two-stage furnace would operate at either 0 MPH, 50 MPH or 100 MPH.

Modulating: Systems with a modulating furnace installed have an infinite amount of stages that they operate under within a preset range. This provides maximum efficiency and superior, consistent comfort when it comes to heating your home. Your everyday car is an example of a modulating condition; it can operate at a variety of speeds and gently accelerate or decelerate depending on what your needs are.


Which is the Best?

While it may seem like there’s a clear winner in using an infinite amount of stages, the high upfront cost of the initial purchase can make a one-stage or two-stage furnace a better choice for you.


Typically, areas with mild winters that only require heating for a week or two can get by with a cheaper single-stage furnace without noticing much in the way of efficiency or performance losses.

If you have mild winters that aren’t incredibly cold but last for a majority of the season, a two-stage furnace can provide the flexibility for multiple operating conditions, increased efficiency over a single-stage, and a noticeable price difference in the initial purchase, while still reaping overall savings in the long run.

If you’re in the market for the best, most efficient, highest-performing unit and are less concerned about the upfront cost, a modulating unit is a clearly superior choice. These units provide the maximum efficiency, extending the life of your system and reducing the wear and tear that comes with single- and two-stage units.


NEXT: How to Pick the Perfect Furnace