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What Causes Furnace Airflow Problems?

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Airflow is an essential part of the regular operation of any furnace. Adequate airflow serves three roles in a typical residential furnace:

  • Remove exhaust gases from the combustion chamber and move them outside
  • Distribute warm air to each room in your house
  • Prevent overheating problems at the heat exchanger or other components

Problems with airflow can cause your furnace to shut down or fail to ignite at all. In severe cases, restricted airflow may damage costly components or even make your furnace unsafe to operate. Recognizing why these problems occur and how to address them can help keep you warm all winter long without the need for expensive repairs.

Blowers vs. Draft Inducers

Modern furnaces use two separate blowers to provide airflow for two very different purposes. The draft inducer (or draft blower) creates negative pressure in the exhaust vent. This vacuum pulls combustion gases away from the chamber and exhausts them outside the home, helping to increase furnace efficiency and safety.

The primary blower is what's responsible for distributing heat throughout your home. This fan pushes air across the heat exchanger, picking up heat and moving it where it's needed. In the process, it also keeps the heat exchanger cooled, which prevents it from cracking and releasing dangerous combustion gases into your home.

Recognizing Airflow Issues

Severe airflow issues with either system will usually cause your furnace to trigger a safety shut down. Safety switches in the furnace can detect a lack of negative pressure from the draft inducer and overheating conditions at the heat exchanger. In both cases, the safety switch will trigger, and your furnace will shut down, at least for a while.

You can usually identify airflow issues with your primary blower if you notice weak or inconsistent air coming from your vents. On the other hand, problems with the draft inducer may be more challenging to spot. A furnace with a faulty draft inducer may trigger an error code that you can read, or you may have to listen for the draft inducer engaging (or not) when the furnace turns on.

Common Causes of Airflow Issues

Airflow issues usually result from a failed blower motor or an obstruction. Draft inducer obstructions commonly occur when rodents, birds, or other animals enter the exhaust vent. These obstructions can reduce airflow, preventing the safety switch from giving the furnace the "all clear" signal to ignite. A bad inducer motor or a faulty safety switch are also potential causes.

Airflow issues with your primary blower typically result from clogged or dirty filters, so replacing your air filter should often be your first step. Furniture or other obstructions near return vents are also typical culprits. If these simple solutions don't work, you'll most likely need a technician to check your blower motor and provide a further diagnosis.

For more information about furnace repair, contact a local technician.