What Is a 2‑Stage Furnace?

If you’re in the market for a new furnace, you may have read about furnace stages in your research.

“Stages” refer to the fuel valve in a furnace. The fuel valve is the part that regulates the flow of natural gas into the burner system.

A 2-stage furnace has an advanced fuel valve that allows the system to operate at a lower capacity when the weather is mild, which provides benefits such as improved comfort and lower energy costs.

In this article, we’ll explain:

  • How a 2-stage furnace works
  • The benefits of a 2-stage furnace
  • How to choose the right furnace for your home

Let’s start by taking a look at how a 2-stage furnace operates.


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How a 2-stage furnace works

A diagram of how a single-stage furnace works / National Renewable Energy Laboratory

To understand how a 2-stage furnace works, first, you need to understand how a basic, single-stage furnace operates.

In a standard furnace, the fuel valve only has two positions: fully open and fully closed.As a result, the furnace always runs at 100% capacity while it is heating your home. It will always run at the same capacity no matter the outside temperature.

Running at full blast is great when the weather is frigid, but that’s not always necessary if the weather is relatively mild. In fact, running on full blast during mildly cold days wastes energy and wears out the furnace equipment faster.

Luckily, a 2-stage valve solves this issue. The valve in a 2-stage furnace has a unique “low fire” (low heat) setting, which allows the furnace to run about 70% of its full capacity on mild days. Running at a lower capacity provides several benefits, which we’ll explain below...

The benefits of a 2-stage furnace

Because a 2-stage furnace can run at a lower capacity on mild days, it provides benefits such as:

  • Increased energy efficiency: The low heat setting on a 2-stage furnace helps the system use less energy, which reduces monthly utility costs.
  • Better comfort: On its low heat setting, a two-stage furnace runs longer, which helps to circulate air to every part of your home. Your home will have more consistent temperatures and fewer random hot/cold spots.
  • Improved indoor air quality: The longer your furnace runs, the more airborne pollutants your air filter pulls through it.
  • Quieter operation: Since a 2-stage furnace does not have to run at full blast all of the time, it is naturally quieter than a single-stage system.
  • Longer-lasting equipment: A single-stage furnace always operates at 100% capacity, which significantly strains the equipment. On the other hand, a 2-stage furnace can run at 70% capacity most of the time, so it will typically last longer than a single-stage unit.

How to choose the right furnace for your home

For most homeowners, the question of choosing between a single-stage and 2-stage furnace comes down to price.

If you are on a tight budget, you may opt for a single-stage furnace because it will cost less upfront. The good news is that a single-stage furnace from a reputable brand will still keep your home comfortable during the winter.

That said, we still recommend 2-stage furnaces over single-stage systems because they offer the benefits we listed above. Even if a 2-stage system costs more upfront, you can save money in the long run because these systems are more energy-efficient than a single-stage furnace.

A professional can help compare the upfront and long-term costs of each type of furnace so that you find the right furnace for your budget and comfort needs.

Want a furnace recommendation from a Portland heating expert?

Contact Four Seasons today to install a high-efficiency, two-stage furnace

Call Four Seasons today at 503-538-1950 or schedule an appointment online for a furnace installation. For over 40 years, we’ve helped Portland residents find the perfect heating systems for their homes. We’re happy to provide you with honest furnace recommendations and excellent customer service backed by hundreds of 5-star reviews.

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