Difference Between Upflow and Downflow Furnaces

When you're choosing a new furnace for your home and looking at upflow vs. downflow furnaces, what should you know? The difference between upflow furnaces and downflow furnaces has to do with the direction of airflow through the furnace and into the home.

We've compiled everything you should know about upflow and downflow furnaces. We'll cover how upflow & downflow furnaces work, what to consider, and how to choose the right one for your home.

Upflow & Downflow Furnace Differences

When choosing between upflow or downflow furnaces, there are some important things to consider. First, what's the difference between upflow and a downflow furnaces? In an upflow furnace, air comes into the furnace from the bottom. It gets heated and then flows upward into the home's ductwork. In a downflow furnace, the air flows in the opposite direction. It enters the furnace from above and flows down into the home.

Choosing Between Upflow & Downflow Furnaces

Considerations When Choosing a Furnace

So, what should you know before deciding which is best for your situation? Here are the most critical considerations:

  • Energy efficiency: In many cases, upflow furnaces are the more energy-efficient option, but this can depend on your location and local climate. This is because heat naturally rises, and this system takes advantage of this natural heat flow. If you're looking for a "greener" option and live in a cooler climate, go with an upflow furnace. However, downflow furnaces can be the more efficient choice for hotter climate areas.
  • Building costs: You should consider where the furnace unit will go in the home and any extra building costs needed to accommodate the furnace. For example, if you have an existing basement, it isn't a concern, but adding a crawlspace or basement just to create room for a furnace can increase the total project cost. If you're installing a furnace in an attic space, you may need to reinforce the flooring, which can add to the cost of this type of project.
  • Challenges with installation: Aside from the costs, it's also important to consider additional challenges. Installing a downflow furnace may come with more difficulties and building code requirements.
  • Location preferences: After all of the other considerations, it may just come down to what the homeowner prefers. Some people prefer to have the furnace in the basement, and others may want to use the attic space. Additionally, the homeowner may also have preferences regarding the vent system and if the warm air should be coming from below or above.

Downflow Furnaces

The main distinction between upflow and downflow furnaces is the direction of the airflow in the furnace. In a downflow furnace, air is warmed as it flows down through the unit and the home's ductwork. This type of furnace is generally placed in an attic or the highest level of a home if there is no attic. Placing the furnace in the attic or upper level gives greater versatility to homes without basements. However, the downward flow of air goes counter to how heat naturally rises, so they are somewhat less energy efficient for heating than upflow furnaces.

Downflow furnaces are popular in the southern portion of the U.S. where the climate is much warmer, and for a good reason. This type of furnace is more energy efficient in this climate, where the cooling season is longer and more humid.

How Downflow Furnaces Work

In a downflow furnace system, the main unit is typically installed in an attic space or on the home's uppermost level. Within a downflow furnace, the blower is located at the top of the unit, and the combustion chamber is below.

When a downflow furnace is in heating mode, it pulls in cooler air through the top of the unit and blows it downward through the combustion chamber. In the combustion chamber, gas burners heat the air moving through the system. The blowers keep the downflowing air moving through the HVAC system and into the ductwork of the home. With downflow furnaces, the air vents are generally in the ceiling or near the tops of the walls in each room, and the warm air is blown down from above.

When downflow furnaces are part of an HVAC system that also includes air conditioning, and the system is in cooling mode, it runs more efficiently. This is because the cooler air naturally sinks downward, and the warm air rises in the rooms. It's then easier for the HVAC system to pull the warmer air up and out of the rooms and push the cooler, air-conditioned air back down into the rooms.

Benefits of Downflow Furnaces

Benefits of Downflow Furnaces

Downflow furnaces are a great choice for specific types of homes in certain climates. Here are the main benefits of downflow furnaces:

  • Perfect for homes without basements: Not every house has a basement, and downflow furnaces are ideal for these homes, with their attic or upper level placement. No need to install an expensive basement when it's not needed or wanted for the home.
  • Efficient for warm climates: Because the airflow in downflow furnaces fights against the natural flow of heat when in heating mode, it's not a good choice for areas with cold climates and long winters. However, these systems are highly efficient when in cooling mode and are excellent for areas with warmer climates and longer warm-weather seasons where the cooling is used more than the heating part of the HVAC system.
  • Lower energy costs in the summer: Downflow furnaces are most efficient in warm weather, so in the hot, humid summer months you can expect some savings in energy costs to cool your home.

Upflow Furnaces

Upflow furnaces work in the opposite way from downflow furnaces. Although the basics of how a furnace works are generally the same, the airflow direction through the HVAC system is the opposite. In an upflow furnace, the air enters the main unit from the bottom and is pushed up through the furnace and into the ductwork. Because of how upflow furnaces function, they are usually placed in basements or crawlspaces underneath the main living spaces of a home.

Upflow furnaces take advantage of the natural tendency of heat to rise and are best for homes in the country's northern areas, where the heating season is typically longer than the cooling season. Homes in these areas are also more likely to have a basement or crawlspace, perfect for installing this type of furnace.

How Upflow Furnaces Work

Upflow furnaces are usually installed in the basement of a home or sometimes in a crawlspace. Because they utilize the natural ability of heat rising, they need to be placed underneath the home's main living areas or on the lowest level available.

In an upflow furnace system, air is pulled in from the return ducts into the bottom of the furnace unit. The cooler air enters the furnace, propelled by the blower, and is warmed as it passes through the combustion chamber. Often powered by gas, the burners in the combustion chamber heat the air in the furnace, and the blowers push the heated air up into the home's ductwork. Most upflow gas furnace systems have air vents in the floors or near the bottom of walls, which allow the heat to rise through the room.

When used for heating, upflow furnaces are very efficient because of air's tendency to rise as it warms. When air conditioning is used in an upflow furnace system, it's not as efficient because the opposite effect is happening in the air. This means that these furnace systems are great for areas with longer heating seasons and shorter cooling seasons.

Benefit of Upflow Furnaces

Upflow furnaces are perfect for certain homes and climates. Here are the main benefits of upflow furnace systems:

  • Energy efficient for heating: Upflow furnaces work with the natural flow of heat going upwards rather than working against it. For this reason, they are the most efficient systems for any homes located in colder climates or areas that have longer seasons where heating is necessary.
  • Great for homes with basements: Upflow furnaces are easily installed in homes with existing basements. There's no need for attic installation or extra flooring work in the attic. Crawlspaces may also be used in homes without full basements.
  • Lower energy costs in winter: Lower costs are a great perk for homes located where the heating season is extra long. Because upflow furnaces are more efficient for heating, you'll see lower energy costs during the colder months.
  • More heating comfort: Because the heated air comes in at the floor level of the interior rooms and rises, many people find this to feel warmer and more comfortable inside the home.
How to Determine the Airflow Direction of your Furnace

How to Determine Your Furnace Airflow Direction

If you've got an existing furnace in your home, and you're wondering about the HVAC airflow direction, here's how to figure it out. First of all, your HVAC unit's placement can give you a good idea of the airflow direction. Furnaces located in an attic or upper story are most likely downflow furnaces. When it's located in the basement or crawlspace of the home, you likely have an upflow furnace.

Even when you know where the furnace is, sometimes it's not easy to determine the direction of the airflow in your furnace. It's important to understand the direction of airflow through your furnace when it's time to change out the air filters. Most furnace filters will have an arrow on one side. When you're changing the filters, you need to make sure the arrow points toward the furnace and away from the return air ducts. This ensures proper placement of the filters so they can catch the dust and other particulates from the air.

Both upflow and downflow furnaces are called forced-air HVAC systems. The air always flows from the return air ducts, through a filter, through the furnace and back into the home. In an upflow system, the air enters the furnace at the bottom of the unit. In downflow furnaces, air enters at the top of the unit. Follow your ductwork to help you determine the direction of the airflow. Once you figure out your airflow, you can draw a couple of arrows on your furnace with a permanent marker to show the correct direction. That will also make future filter changes easier.

Upflow vs. Downflow Furnaces Price Difference

If you're comparing upflow vs. downflow furnaces and wondering about the differences in cost, the short answer is that the furnaces themselves are priced very similarly. And for the most part, any price variations won't matter much. The type of furnace that's right for your home will largely depend on the climate where you live and the type of home you have. If you live in the far south, you'll likely be looking for a downflow furnace. Colder areas of the northern states will need upflow furnaces.

It's important to remember that each type of furnace is more efficient in different functions. So, the furnace that's right for your area can help save you on energy costs. Upflow furnaces are more efficient for heating and will have lower operating costs for areas with longer heating seasons. Downflow furnaces are more efficient during the cooling months and will save the homeowner on energy during warm weather.

Downflow furnaces are priced very similarly to upflow furnaces. However, if this is the first furnace you're purchasing for a new home, consider where in the house the furnace will be located. If any additional construction would be necessary, that could affect your choice. Adding a basement to a new home design or installing flooring to support an attic furnace safely could be necessary.

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Browse the Selection of Upflow & Downflow Furnaces on IWAE

Ingrams Water & Air has you covered for all your furnace shopping needs. We offer a wide variety of all types of furnaces and HVAC systems. Plus, our knowledgeable staff can help make your decision easy. Whether you need an upflow furnace or a downflow furnace, we have the top quality brands and technical support to ensure you get the right furnace for your home. Browse our furnace selection today or contact us with any questions about choosing the right furnace for you.

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