Why Is My Furnace Blowing Cold Air?

If your furnace is blowing cold air sometimes, your Montgomery, AL, home certainly isn’t as comfortable as it could be. One moment, it seems like your heating system is running just fine – then the next, you’re met with an icy blast of air from your ducts when you expected warm air.

There are several reasons that could be behind a furnace that’s blowing cold air. Sometimes, the issue is the result of a simple error – in other situations, you need to call a professional for heating repairs. In our most recent blogs, the technicians at Hans Heating & Air discuss what makes a furnace blow cold air and what needs to be done to fix it.

Reasons a Furnace Is Blowing Cold Air Sometimes

If your furnace was working just fine but now you notice cold air coming from the vents throughout your home, look into thermostat and airflow issues before calling your HVAC repair company for service.

Wrong Thermostat Settings

It’s the thermostat’s job to send instructions to your heating and cooling system, telling it when to heat, when to cool, and when to run its fan. A simple enough reason a furnace is blowing cold air sometimes is that the wrong thermostat settings are in use. Make the thermostat your first stop as you troubleshoot this issue.

  • Make sure the thermostat is set to HEAT, not COOL. If someone accidentally bumped the thermostat or set it incorrectly, the reason why you feel cold air from your vents may be because your air conditioner is running – not your furnace.
  • Check the thermostat’s fan settings and make sure AUTO is selected, not ON. The ON setting allows your HVAC system’s blower fan and motor to operate continuously, even when the furnace is not heating. Between heating cycles, the blower will continue to circulate air through your ducts; it just won’t be hot because the furnace isn’t running to create heat. The AUTO setting enables the blower to run only as the furnace also cycles. Using the AUTO setting not only clears up the uncomfortable issue of a furnace blowing cold air sometimes, but it requires far less energy consumption than a fan that runs 24/7.

Airflow Restrictions

If the air coming from your supply vents feels cool and airflow also appears weak, the system’s airflow may be obstructed. To work properly, ample airflow is required by the furnace – blockages within the furnace, the duct system, or vents impede air movement, causing the system to struggle as it attempts to push heat into your home. 

  • A dirty furnace air filter is a common culprit of an airflow restriction. When the air filter is caked with dirt and debris, these contaminants restrict air movement through the air filter and into the furnace. Check your air filter on a monthly basis, and change it at the recommended interval or sooner if needed.
  • An obstruction in the duct system can cause a weak stream of cool air in vents supplying a room or area of the home. Usually, a duct run has been damaged, has fallen, or has become disconnected. You may be able to patch this up yourself, or choose to leave it to the pros who can easily work in those tight areas where ducts often run.

Dirty Flame Sensor

A gas furnace has a flame sensor that detects the presence of a flame created by burning fuel. This safety control shuts down the heating system if it cannot detect a flame in the burner assembly while gas is feeding into the furnace. Soot from combustion can cover the component, inhibiting its ability to detect a flame.

Your furnace may have been generating heat just fine one minute, but then the flame sensor shut down the heating cycle – in this case, you sometimes have cold air blowing from your furnace because the blower continues to run its cycle, absent of heat production. This delicate component can be cleaned by a technician in some cases, or it may need to be replaced to avoid further malfunctions.

Pilot Light or Ignitor Malfunction

Older furnaces may be equipped with pilot lights, while newer models use an electric ignitor to spark gas for combustion. If the pilot light goes out or the ignitor fails, the gas doesn’t ignite, which can lead to cold air blowing from the furnace. Follow the instructions in your furnace owner’s manual to safely relight the pilot – if it continues to go out, call for furnace repair. If your unit uses an ignitor, call for service to have the broken component replaced. Don’t worry, ignitors typically have to be replaced every seven years or so.

Stop Cold Air Coming from Your Furnace

A furnace that blows cold air isn’t reliable and won’t get you through the winter with the warmth you need. When troubleshooting doesn’t stop the issue, call Hans Heating & Air for fast furnace repair. For all of your heating and air conditioning needs, contact Hans today.

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