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The Difference Between a One-Stage and a Two-Stage Furnace

one state vs two stage furnaceIf you’ve ever had to install or replace a heating system for your home in Oswego, Yorkville, Naperville, Aurora or Plainfield, you may have heard the terms “single-stage furnace” and “two-stage furnace” before. If not, that’s okay – you’re not alone. These can be words you might hear more often during a sales discussion.

Whether you’re familiar with them or not, we’ll discuss them here to help further your understanding of the difference between a one-stage and a two-stage furnace.

Single-Stage Furnace

A standard single-stage gas furnace operates at one capacity. In other words, it will run the same way regardless of the degree of cold outside. An Amana model with a 100,000 BTU rating would run at 100,000 BTUs whether the temperature is 2 or 32 degrees.

A main advantage of a single-stage furnace over a two-stage unit is that is overall less likely to malfunction, and if it does, it is usually less expensive to repair.

The single-stage furnace’s parts are also typically more common and lasting. If 10 years from now your HVAC service provider needs to locate a part for maintenance or repair of your furnace, there’s a good chance the part will be available.

Two-Stage Furnace

A two-stage gas furnace has two levels of heating output: high fire and low fire. The first stage (low fire) is the primary one that runs about 75% of the time or more. The second stage (high fire) will typically activate when it’s icy cold outside. It will also turn on if the thermostat senses it needs to raise the temperature more than two degrees.

We’ll return to our BTU example. You have a two-stage Amana furnace with a 100,000 BTU rating. When it first starts up, it will run at 75,000 BTUs (75% of 100,000). If after running for several minutes the unit determines it is not keeping up with the need for heat, it will switch to the high-fire stage to supply what’s required.

Some common advantages of a two-stage furnace you might hear discussed include the following.

Consistency. Two-stage furnaces run for longer, steadier periods than single-stage furnaces do. This lets them better regulate the home’s interior temperature. A single-stage unit sends out bigger blasts of heat when it turns on, which can create greater fluctuations in the interior temperature.

Efficiency. Because two-stage furnaces can operate at a lower setting based on the actual heat required, as well as spend more time at that setting, they can often use less fuel than standard furnaces, which turn on and off (cycle) more frequently. 

Quiet. Single-stage furnaces’ more-frequent cycling also means they can make more noise. They are typically louder when running at full throttle as well. Two-stage units can be less noticeable by not cycling as much, and many models can be quieter than single-stage units when operating at full blast.

Less-frequent cycling likewise contributes to less system stress and longer system life. 

Air Quality. Because two-stage furnaces run for longer periods than single-stage units do, they spend more time trapping impurities in their filters.

So Which Is Better for Me?

Either a single-stage or a two-stage furnace may be a fit for what you need to keep your home comfortable and warm with reasonable energy costs. What’s important is that you understand the differences between them when you’re discussing your choices.

With today’s advances in technology, in some cases a new single-stage model might serve you just fine, depending on the model. Heating efficiency is determined by the heat-exchanger design. One- and two-stage furnaces that have the same efficiency style often use the same heat exchanger, so it’s possible that a 97% efficient single-stage furnace will perform the same as a 97% two-stage model.

Contact Us Today 

The key to choosing the right model for your home comes down to your relationship with your HVAC professional. A local service provider with a connection to your community will look to identify important variables such as home size and needed heat output to help you decide on your furnace.

If you would ever like to further discuss the difference between a one-stage and a two-stage furnace for your home in Oswego, Yorkville, Naperville, Aurora or Plainfield, please feel free to call (630) 731-1550. An Air Dynamics heating an air-quality specialist will be glad to hear from you and assist you.

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