What's The Difference Between One Stage and Two Stage Furnaces?
Published 2/20/2025
The difference between a one-stage and a two-stage furnace has to do with how they operate in regard to heating output and efficiency. Before going in-depth about these systems, it's best to first understand what furnace stages are and what they mean for buyers. Deciding which stage type to choose can depend on your climate, budget, and more.
Furnaces are classified based on how they operate when heating your home or building. The "stage" refers to how many levels of heat output the furnace can produce. One-stage furnaces have only two settings: On (100% capacity) or Off. Two-stage furnaces have two heat settings: low stage (~60-70% capacity) and high stage (100% capacity). Another key factor in comparing these stage types is their AFUE rating. In this article, we will look into the main differences and discover which type of furnace is best for your property.
What is Annual Fuel Utilization Efficiency (AFUE)?
AFUE (Annual Fuel Utilization Efficiency) measures how efficiently a furnace converts fuel into usable heat over a year. This number is expressed as a percentage and indicates the amount of fuel energy that is actually used for heating versus what is lost through combustion and exhaust. For example, a furnace with 80% AFUE converts 80% of the fuel into heat, while 20% is lost through the flue. Prioritizing a high AFUE rating is common when considering furnace replacement services.
Single-Stage Furnace
Single-stage or one-stage furnaces are traditional systems that date back to the early 20th century. This type of furnace relied on gas combustion, single-speed blower motor, and simple thermostat control. As previously mentioned, a single-stage furnace has two settings: On and Off. When set to On, the heating system runs at full blast until the temperature is reached. Because of frequent cycling behavior, the one-stage furnace can lead to greater fluctuations in indoor climate. AFUE ratings for single-stage furnaces typically range from 80% - 92%. Many furnace replacement services stem from these older, less efficient models.
Key advantages of choosing a single-stage furnace include:
- Lower upfront cost
- Simple maintenance
- Faster heating
- Easier installation
Two-Stage Furnace
Two-stage furnaces were introduced in the 1980s and 1990s as part of an industry shift toward energy efficiency. This type of furnace became more popular over time as the Department of Energy (DOE) set standards that encouraged the adoption of furnaces that use less energy. Other benefits to homeowners included consistent temperatures and quieter operation. There have also been advancements in gas valve technology, allowing for more precise fuel control. It's also worth mentioning that two-stage furnaces tend to have less cycling frequency, which can reduce strain on components and lead to a longer lifespan. AFUE ratings for two-stage furnaces typically range from 90% - 98%. This is why homeowners seeking furnace replacement services choose to upgrade to a two-stage furnace.
Key advantages of choosing a two-stage furnace include:
- More consistent indoor temperature
- Higher energy efficiency
- Quieter operation
- Smart thermostat compatibility
Maintenance for Single Stage and Two Stage Furnaces
Proper maintenance for your furnace ensures longevity. Both stage types should have an inspection once a year by a NADCA-certified HVAC company like Mr. Duct. Furnaces should also have their filters changed every 3 months to reduce strain on the heating system. Other maintenance steps, such as inspecting the heat exchanger and lubricating moving parts, should be accomplished by a trusted HVAC contractor. If you're experiencing issues with your furnace, contact an HVAC company. Check out our blog article to learn common signs that signal you need furnace replacement services.
Which Furnace Heating Stage Type is Right For Me?
Choosing the right stage type for your furnace can depend on several factors, including your location's climate, home size, operating costs, and noise levels. If you live in a mild climate area, a one-stage furnace may be sufficient. If you experience harsh winters like the ones in the Chicagoland area, a two-stage furnace may be a better fit. From an HVAC contractor's perspective, two-stage furnaces require a more advanced thermostat and additional ductwork considerations. For homeowners looking to stay long-term, a two-stage furnace may also pay for itself in energy savings over time. Learn about Mr. Duct's furnace replacement services to find out which stage type is best for you.
Why Choose Mr. Duct HVAC Services
Mr. Duct HVAC services have served the Chicagoland area for over 20 years. Many homeowners choose to work with us because of our upfront and honest pricing during our quote process. With a team of 50+, our staff is dedicated to taking great care of your heating and cooling needs. Mr. Duct is also an authorized Trane® dealer, ensuring you get a heating system that works best for you. Learn more about our HVAC company's furnace services here.
Schedule Furnace Repair, Replacement, & Cleaning in Glen Ellyn, IL & Surrounding Areas
Whether you are looking for furnace repair, furnace replacement services, or HVAC cleaning, our NADCA-certified technicians will be able to assist. Our HVAC company services all Chicagoland areas, with locations in Lisle, Naperville, Glenview, and more. Check out our furnace service coupons, then contact Mr. Duct today to schedule your furnace service or request a quote!