Downflow vs. Upflow Furnaces and What You Should Know Before Buying

By Mike Haines 1/29  Choosing the right furnace for your home can feel overwhelming. With so many terms like “downflow,” “upflow,” “variable speed,” and “modulating,” you might wonder how all of these factors come together to affect your heating system’s efficiency and performance. In this post, we’ll compare two excellent furnaces from Goodman—one designed for downflow installations and the other for upflow. Our goal is to clarify not only what these furnace orientations mean, but also to help you decide which option best suits your home heating needs.

The Difference Between Downflow and Upflow Furnaces

Below, we’ll explore two specific models available on ACDirect.com:

• Goodman Downflow 80,000 BTU 97% Efficient Modulating Variable Speed ECM Gas Furnace (R32-GDVM970804CN)
• Goodman 80,000 BTU 96% Efficient Gas Furnace Upflow Variable Speed California Ultra Low NOx (R32-GR9S960805CU)

By the end of this blog post, you’ll have a clear understanding of the differences between downflow and upflow furnaces, plus insights into which configuration might be ideal for your home.

Key Highlights

Downflow Furnace: Goodman 80,000 BTU 97% Efficient Modulating Variable Speed ECM Gas Furnace (R32-GDVM970804CN)

• 97% AFUE Efficiency: Converts 97% of fuel into usable heat, minimizing energy waste.
• Modulating Gas Valve: Ensures precise temperature control for consistent comfort.
• Variable Speed ECM Motor: Provides quieter operation and enhanced energy savings.
• Best For: Attic installations or homes with ductwork located below the furnace.

Upflow Furnace: Goodman 80,000 BTU 96% Efficient Gas Furnace Upflow Variable Speed California Ultra Low NOx (R32-GR9S960805CU)

• 96% AFUE Efficiency: Delivers outstanding fuel efficiency while reducing heating costs.
• Ultra Low NOx Compliance: Ideal for areas with strict environmental regulations like California.
• Variable Speed Blower: Offers better airflow control and enhanced indoor air quality.
• Best For: Basements, ground-level utility closets, or homes with ducts above the furnace.

What Does Furnace Orientation Mean?

Furnace orientation refers to the direction in which the heated air flows out of your furnace:

1. Downflow Furnace – Forces heated air downwards, typically installed in attics or upper levels of a home.
2. Upflow Furnace – Pushes heated air upwards, typically installed in basements or lower-level utility rooms.

While this might sound like a simple matter of which direction the air goes, orientation can significantly impact system performance, efficiency, installation costs, and comfort. The placement of your furnace, the design of your home’s ductwork, and factors like climate and local regulations can all play a role in determining which furnace orientation is right for you.

Downflow Furnaces

What is a Downflow Furnace?

A downflow furnace is designed to draw cool air in at the top and expel warmed air at the bottom. These are typically installed in locations where ductwork is below the furnace—often in attics, or on the main floor of a home where the hot air needs to move downward to the living spaces.

How Does a Downflow Furnace Work?

When the thermostat calls for heat, the furnace’s blower pulls cool air from the top. This air passes through the heat exchanger, becoming warmed before it is pushed down through the furnace’s outlet and into the ductwork situated below. The air then circulates through the ducts, distributing warmth throughout the home. By the time it returns to the furnace, it has cooled slightly and is ready to be reheated, completing the cycle.

Ideal Installation Scenarios for Downflow Furnaces

• Attic Installations: Homes with enough attic space (or a dedicated attic utility area) are prime candidates for a downflow furnace, as the unit can be positioned so that ductwork naturally flows downward.
• Homes Without Basements: In regions where basements are uncommon or the water table is high, furnaces are often placed in a top-floor utility closet.
• Split-Level Homes: In certain multi-story homes, a downflow system can be more efficient for distributing heat evenly across levels.

Benefits of Downflow Furnaces

1. Simpler Duct Routing in Certain Homes: If your ductwork is already installed beneath the attic floor, a downflow furnace offers a straightforward connection.
2. Space-Saving: In an attic installation, the furnace occupies space that might otherwise go unused. This arrangement can free up rooms on the lower floors.
3. Potential for Better Air Distribution in Upper Floors: Since warm air naturally tends to rise, starting higher up can help regulate temperatures in multiple levels.

Upflow Furnaces

What is an Upflow Furnace?

An upflow furnace intakes cool air at the bottom and releases warmed air upward. These units are most commonly installed in basements, crawl spaces, or utility closets on the ground floor.

How Does an Upflow Furnace Work?

The furnace’s blower pulls cool air in from the bottom. After the air is heated by the heat exchanger, the blower forces this warm air upwards into the duct system. From there, it flows to vents throughout the home. Eventually, when the air cools, it cycles back down to the furnace for reheating, maintaining a consistent temperature.

Ideal Installation Scenarios for Upflow Furnaces

• Basement Installations: If you have a full basement, an upflow design often provides the simplest ductwork routing—hot air moves upward to the living areas.
• Crawl Spaces: Some homes feature crawl spaces that allow the furnace to be neatly tucked below the main floor.
• Utility Closets in Lower Levels: In regions where basements might be partial or nonexistent, a ground-floor closet is often used.

Benefits of Upflow Furnaces

1. Accessibility: Maintenance and repairs can be easier, as basements and lower-level closets are often more accessible than attics.
2. Efficient Heating for Above Floors: Because warm air naturally rises, pushing heated air upward can feel intuitive for overall comfort in a multi-level home.
3. Familiar Option in Many Homes: Historically, upflow designs have been the “standard” for houses with basements, making them common and widely recognized.

Key Differences to Consider

Airflow Direction

• Downflow: Air is taken in from the top and expelled at the bottom.
• Upflow: Air is taken in from the bottom and expelled at the top.

Installation Location

• Downflow: Typically found in attics or the topmost levels of a home.
• Upflow: Typically found in basements, crawl spaces, or ground-level utility closets.

Ductwork Requirements

• Downflow: Ducts run below the unit, potentially more straightforward in top-floor installations.
• Upflow: Ducts run above the unit, typically efficient in basement installations.

Efficiency and Performance

Both downflow and upflow furnaces can reach high efficiency ratings (such as 96% or 97% AFUE). However, the actual efficiency you experience depends not just on the unit’s official rating but also on how well-suited the orientation is to your home’s design and ductwork layout. Mismatched orientation could lead to inefficiencies or more complex duct layouts.

Highlight: Goodman Downflow 80,000 BTU 97% Efficient Modulating Variable Speed ECM Gas Furnace (R32-GDVM970804CN)

High-Efficiency Operation

When you see a 97% efficiency rating, it means that this furnace converts 97% of its fuel into usable heat. This is among the highest available in the residential market. The modulating capability adjusts the furnace’s heating output in small increments, maintaining a more consistent temperature. This not only improves comfort but can also reduce energy costs over time.

Variable Speed ECM Motor

The variable speed ECM (Electronically Commutated Motor) further enhances efficiency by running at different speeds based on your home’s current heating demands. Instead of blasting air at one speed, the furnace can precisely modulate airflow to maintain even temperatures and reduce hot or cold spots.

Benefits of a Downflow Modulating Furnace

1. Consistent Comfort: The modulating gas valve and variable speed motor work in tandem to keep indoor temperatures stable—no more abrupt temperature swings.
2. Quieter Operation: Unlike single-speed motors that go full-throttle at all times, a variable speed ECM runs at lower speeds for longer periods, significantly reducing noise.
3. Top-Tier Fuel Efficiency: At 97% AFUE, a significant portion of your heating budget translates directly into warmth, meaning less waste and fewer emissions.

Ideal Use Case

If your home’s duct system or layout requires air to be blown downward—whether in an attic installation or upper-level closet—this Goodman Downflow 80,000 BTU 97% Efficient Furnace is an excellent choice. Its high AFUE rating and advanced technology ensure performance efficiency and comfort.

Highlight: Goodman 80,000 BTU 96% Efficient Gas Furnace Upflow Variable Speed California Ultra Low NOx (R32-GR9S960805CU)

96% AFUE Rating

With a 96% AFUE rating, this Goodman upflow furnace is extremely efficient, converting most of its fuel into heat. The small difference in efficiency rating from 97% to 96% will have minimal impact on utility bills but can be significant in terms of cost savings compared to older, less efficient models.

Variable Speed for Comfort

A variable speed blower adjusts airflow to meet the exact heating needs, maintaining more even temperatures and offering quiet operation. Variable speed technology also improves the air quality in your home by allowing the furnace to run longer at lower speeds—great for filtering and dehumidification (when paired with compatible systems).

California Ultra Low NOx Compliance

One of this model’s standout features is its California Ultra Low NOx compliance. If you live in an area with strict emissions standards, such as California or certain local jurisdictions, this certification is essential. Ultra Low NOx technology helps significantly reduce nitrogen oxide emissions, contributing to cleaner indoor and outdoor air.

Ideal Use Case

For those with a basement or ground-level installation setup, the Goodman 80,000 BTU 96% Efficient Upflow Furnace is a fantastic choice—especially if you need to meet stringent emissions regulations. Its robust efficiency, ultra low NOx emissions, and variable speed blower make it both cost-effective and environmentally friendly.

Choosing the Right Furnace for Your Home

1. Evaluate Your Home’s Design

The very first step is to look at where your existing furnace is located and how your ducts are laid out. If you already have an attic furnace setup, a downflow furnace might be the simplest replacement. Conversely, if your existing system is in the basement, an upflow furnace is usually the most straightforward option.

2. Consider Local Building Codes and Regulations

Different regions have different requirements. Some places mandate low NOx or ultra low NOx furnaces. Make sure you verify your local emissions standards to ensure compliance. If you’re in California or another state with stricter emissions standards, the R32-GR9S960805CU (Ultra Low NOx) may be the better option.

3. Think About Energy Efficiency Goals

Both highlighted Goodman furnaces are in the top tier of efficiency. If the difference between 96% and 97% AFUE is meaningful to you for long-term energy savings, you might lean toward the downflow model. However, in many situations, a 96% AFUE rating can be just as cost-effective when factoring in overall installation requirements.

4. Consult an HVAC Professional

It’s always wise to speak with a qualified HVAC technician before making a final decision. They can evaluate your home’s insulation, duct size, and airflow requirements to ensure you select the optimal unit.

5. Factor in Your Budget

High-efficiency furnaces often come with a higher upfront cost, but they can pay for themselves in reduced utility bills. Whichever orientation you need—upflow or downflow—consider the lifecycle costs rather than just the purchase price. Keep in mind that rebates and incentives might be available for high-efficiency or ultra low NOx models, making them even more cost-effective in the long run.

Installation and Maintenance Considerations

Proper Sizing

An 80,000 BTU furnace, whether upflow or downflow, is a solid choice for medium-to-large homes, but proper sizing involves more than BTUs alone. Window types, insulation levels, and climate zones all matter. An improperly sized furnace can lead to inefficiency, short cycling, and premature wear.

Routine Maintenance

Regardless of orientation, a furnace is an investment that requires annual maintenance to sustain peak performance. Routine tasks include:

• Changing or cleaning air filters
• Inspecting the heat exchanger
• Cleaning the burners and blower motor
• Checking for gas leaks or carbon monoxide

Having an annual inspection by a certified professional ensures a long system lifespan and optimal energy efficiency.

Indoor Air Quality Enhancements

Both variable speed and modulating features contribute to better indoor air quality. Longer run times at lower speeds mean more air passes through filters, capturing more pollutants, allergens, and dust. Upflow and downflow units alike can be paired with advanced filtration or air purification systems for a healthier home.

Final Thoughts

When comparing downflow and upflow furnaces, the core difference boils down to airflow direction and installation location. The Goodman Downflow 80,000 BTU 97% Efficient Modulating Variable Speed ECM Gas Furnace (R32-GDVM970804CN) is an outstanding example of a high-efficiency unit perfect for attic or top-floor installations. Meanwhile, the Goodman 80,000 BTU 96% Efficient Gas Furnace Upflow Variable Speed California Ultra Low NOx (R32-GR9S960805CU) offers a similarly high level of performance for homes with basements or ground-level utility closets, along with the added environmental benefit of Ultra Low NOx emissions compliance.

Ultimately, the best choice depends on your home’s duct configuration, local building codes, and your personal preferences regarding energy efficiency and environmental impact. If you’re still unsure which orientation to choose, reaching out to a licensed HVAC professional is the most reliable path to ensure a successful, efficient heating system for your home.

Ready to upgrade your furnace? Explore these two impressive Goodman furnaces and many more on ACDirect.com. Whether you need a downflow or an upflow system, investing in a high-efficiency, advanced furnace will keep your home comfortable and energy bills manageable for years to come.