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When you’re looking at buying furnaces, it’s important to understand what “staging” is. Staging is the ability of a unit to operate at various ‘stages’ of performance. Furnaces are rated in three distinct categories of staging: One-Stage, Two-Stage, and Modulating.

The More Stages, The Better

Modulating, Single Stage & Two Stage Furnaces

Product Expert
The More Stages, The Better

As the summer approaches, you may be considering replacing that old air conditioner in time for the seasonal heat wave. Have you considered replacing your furnace at the same time?

If you can't remember when you last updated your furnace, chances are your system could be due for a furnace upgrade as well.

Often times it’s hard to keep track of when you bought this appliance or that appliance, as well as the age and model numbers of the units.

Replacing major components like the furnace and air conditioner at the same time helps you keep track of how old the system is and how often it needs servicing.

When you’re looking at buying a new furnace, it’s important to understand what “staging” is 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.

When Should I Use What?
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 initial purchase, while still reaping an 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 the 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

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