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Furnace Not Getting Enough Fresh Air? Here’s What To Do

The installation of a furnace should focus on providing proper ventilation from the outside. These units are relatively popular among homes, allowing for better temperature regulation during the winter months. 

If your furnace isn’t getting enough fresh air, you can improve it by looking at the duct size of the fresh air intake, replacing the filters, inspecting the duct runs, and making sure there are no leaks in the furnace. The appropriate fix will depend on the cause of the problem.

With this guide, you will discover some of the causes that could be behind poor fresh air provisioning in your home. We look at common problems that affect the furnace set up and give you effective solutions for each of these causes. 

Ineffective Fresh Air Intake Configuration

The first thing you want to look at is the configuration of the fresh air intake. Many furnaces will use an opening in a duct system that runs toward a specific building area. This area is often the basement, as these rooms are generally used for storage. The inflow of fresh air is then distributed from there toward the rest of the building. 

The air is carried through the system, ensuring a building’s interior does not feel stuffy. When there is a lack of fresh air, you may find the building uncomfortable. While furnaces are generally installed to push fresh air into the building, there are a few issues that can interfere with airflow. 

In some cases, the configuration of the fresh air intake setup may be ineffective. When this is the source of the problem, you will likely find that there is insufficient fresh air in the basement or another room where the air is pushed toward 

How To Fix

Furnace not getting enough fresh air due to the intake configuration can usually be fixed by making a few adjustments at this part of the system. You need to consider why there is a lack of fresh air being pushed in through the intake setup: 

  • Make sure the open duct has enough space to allow fresh air to flow through.
  • Check if anything is blocking the flow of air through the fresh air intake. This could be a simple problem as a storage cupboard standing too close to the duct’s inlet in the basement. 
  • See if there are too many curves and corners inside the fresh air intake duct. If this is the case, airflow may be disrupted as it enters your building. 

Struggling to inspect the air intake unit or not sure how to inspect it? Then this video might be helpful: 

Insufficient Duct Run Sizing

Ducts in a furnace play a crucial role in ensuring there is adequate airflow throughout the entire system. When it comes to looking at fresh air, you will need to consider all ducts throughout the system. 

An inspection of your ducts will be needed. In this particular case, you want to look at the sizing of the ducts used throughout the furnace system. When the ducts are not big enough for your HVAC system’s size and the size of the building, then air cannot flow through efficiently. 

This can cause an increase in pressure within the system too, which may lead to further damage.

How To Fix:

An inspection of the ducts throughout your building is the first step to determining the issue. When you find that there is too much pressure inside the duct, it may indicate insufficient sizing. Smaller ducts are used for compact buildings, whereas a larger system is required when you have a multi-story building:

  • When you find that some parts of the duct run are too small, you will need to remove the existing ducts and install new ones. 
  • Consider the needs of your building. Then choose ducts that have an appropriate size. 
  • When switching ducts, be sure to turn the entire HVAC system off. 

Struggling to replace the ducts in your furnace system with larger alternatives? Be sure to take a look at this video:

Dirty Filters Blocking Airflow

There are different types of particles that may flow into the ducts that are installed throughout your home. This is why filters are used in furnace installations. These filters help to block out the dust and other particles that flow through the ducts. 

Without proper maintenance of the ductwork, the particles will build on the system’s filters. Debris and dust form a layer on top of the filter, which means the opening available for air to flow through becomes smaller over time.

When filters are packed with debris and other particles, some problems can develop. In addition to reducing the distribution of fresh air throughout the building, you may also run into issues like noises and too much pressure in the HVAC system. 

How To Fix:

When the furnace and ductwork filters are blocking airflow, there are two possible solutions. You will need to consider whether you have installed reusable filters. Not all filters are reusable – in this particular case, you will need to get a replacement filter. If your filter is reusable, you might be able to wash the debris layer off and put it back into the furnace:

  • Consider the type of furnace installation you have. You need to identify the areas where filters are found. You might have to unscrew a cover on the main furnace unit. 
  • Remove the filter from the furnace. Clean the filter thoroughly without damaging the filter materials, or get a replacement if it is not reusable. 
  • Place the filter into the appropriate position. Close the cover and make sure to secure it tightly with the screws. 

If you want a visual overview of how filters are replaced in a furnace, watch this video: 

Problems with the Duct Runs

While your furnace is responsible for regulating airflow, your ducts carry the air throughout your building. When there is a reduction in fresh air flowing into your home, it might be time to inspect your ducts for problems. 

Some issues can affect your ductwork. For example, a broken part can cause air to leak into specific areas of your home – leaving the rest of the building without proper levels of fresh air. It is not only broken parts of a duct that can cause problems, however. Consider disconnections and poorly installed parts too. 

How To Fix:

Start by walking along with the ductwork throughout the building. You want to check all parts while the furnace is running:

  • See if you find any areas where the air is leaking out of the ductwork. 
  • You might have to increase the pressure of the furnace a bit. This will ensure parts that leak will blow out more air – making it easier to identify. 
  • Look for cracks and damage to your ductwork too. 
  • When you find problematic areas in the ductwork, it is time to fix the problem.
  • If the duct has runs that are disconnected, simply reconnect these. Make sure they fit perfectly to ensure air does not escape in the future. 
  • If there are problems with the ductwork installation, you might have to find a professional to help reinstall. 
  • When damage is noticed, a replacement of the affected duct runs will be needed. 

While there are some DIY strategies for fixing these problems, working with a furnace without experience can be dangerous. Trying to fix the furnace yourself could also lead to more damage and further issues. 

Final Thoughts

Insufficient fresh air flowing through a furnace system can lead to a stuffy and unpleasant building experience. Causes may include small ducts, not having enough return air vents, and more. Understanding what symptoms to look out for and know how to identify the problem at hand. 


  • Steve Rajeckas

    Steve Rajeckas is an HVAC hobbyist with an avid interest in learning innovative ways to keep rooms, buildings, and everything else at the optimal temperature. When he's not working on new posts for Temperature Master, he can be found reading books or exploring the outdoors.

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