What is a Two Stage Furnace & How Does it Work?

Contractors often use technical terms and specifications to make a sale, and HVAC contractors are no exception. One topic that often comes up is two-stage furnaces and whether they are worth the additional cost. The answer, as you might expect, is that it depends on various factors such as your region’s average temperature and your budget. However, it is clear that two-stage furnaces outperform their single-stage counterparts in many ways.

In this article, we will explore what a two-stage furnace is, how it operates, and the benefits it offers. By the end, you should have a better understanding of whether a two-stage furnace is the right choice for your home.

What is a Two-Stage Furnace?

A two-stage furnace is a gas furnace that offers two levels of heat output. It has a high output for extremely cold days and a lower output for milder winter days. In fact, about 80% of the time, the low setting is sufficient to meet most household heating needs. This results in longer furnace run times and more even heat distribution, eliminating temperature swings.

To achieve this, a two-stage furnace utilizes a different programming set compared to a single-stage furnace. When the interior temperature is moderately cold, the furnace’s control board partially opens the fuel control valve. It then heats the house to the desired temperature before shutting off. On extremely cold days, when the house cools quicker than expected, the control panel fully opens the valve, allowing the furnace to run at full power.

How Does Your Furnace Do This?

While much of the technology behind two-stage furnaces is proprietary, the basic principle is straightforward. The position of the valve depends on how often the thermostat turns the furnace on and off, as well as the temperature difference between the thermostat setting and the actual house temperature. For example, on moderately cold days, the furnace does not require the valve to be fully open.

Think of a two-stage furnace’s operation like the gas pedal in your car. When driving on the Autobahn in Germany, you may need to floor the gas pedal, whereas in heavy traffic in California, you don’t need to apply as much pressure. Similarly, a two-stage furnace can vary the amount of fuel used based on the heating requirements.

How Does a Two-Stage Furnace Work?

A one-stage furnace, also known as a single-stage furnace, has a burner section with a valve that controls the fuel flow. In contrast, a two-stage furnace has three positions for this valve: fully open, partially open, and closed. When the furnace turns on, it can adjust the valve to either of its two open positions.

This allows the furnace to operate at full power or at a lower setting that provides about 60 to 65% of the heating power of the full-open position. As a result, a two-stage furnace offers two heat settings that are automatically used: high heat and low heat.

What are the Advantages of a Two-Stage Furnace?

A two-stage heating system offers three main advantages: energy savings, improved heat distribution, and enhanced air filtration.

Energy Savings

A two-stage furnace saves energy because it burns less fuel. By adjusting the fuel flow based on the outdoor temperature, a two-stage furnace can operate in the partially open position, using only about 60% of the heat output of a single-stage furnace. This is particularly beneficial on moderately cold days when a full blast of heat is not required.

Improved Heat Distribution

A single-stage furnace can cause cold spots in your home due to improperly positioned ductwork, an oversized furnace, or its inability to adjust heat output. In contrast, a two-stage furnace runs at a lower heat setting for a longer duration, distributing heat more evenly throughout the house. This helps eliminate temperature fluctuations and cold areas.

Enhanced Air Filtration

Since a two-stage furnace runs more frequently, it circulates more air through your ductwork, leading to improved air filtration. This is especially advantageous compared to a single-stage furnace or an oversized furnace, which tend to cycle on and off more frequently, reducing the time available for air filtration.

Final Thoughts on Furnaces

Deciding whether a two-stage furnace is the right choice for you depends on your specific needs. However, the additional investment required for a two-stage furnace is undoubtedly worth it. It provides long-term energy savings, eliminates cold spots, and enhances air filtration in your home. If you have any issues with your existing furnace or want to learn more about different heating systems, consider reaching out to Phyxter Home Services for assistance. Additionally, feel free to explore our other furnace articles to further expand your knowledge on home heating systems.