Why Is My Furnace Blowing Cold Air?

Girl in winter clothes is shivering in front of radiator. Fearful expression. Concept for energy crisis or old heating system.

Did you finally turn your furnace on this winter only to have cold air blowing out of your vents? Did your furnace stop working just when you started to need it most? There are a few reasons your furnace may be blowing cold air, and there a few things to check before you need to worry too much. At BlueAir, we are here to keep you warm and toasty this winter. If you are having problems with your furnace, check these things first and then call us for help.

Check to Make Sure the Power Switch is On

By Code, gas furnaces have a power switch next to the unit. This is a safety feature that allows a service person to be sure that there is no electricity to the unit during repairs. Many times people mistake the switch for a light switch and turn it off. It is very common for a repairman from another trade, say the cable guy to switch it off when he is leaving the attic. It is also a common occurrence during the holiday season when people are storing decorations. So, if your furnace isn’t coming on, check the switch first.

Check Your Thermostat

Be sure your thermostat is set on the correct setting. If it is set to “ON,” the blower will run constantly, even when the furnace isn’t heating any air. The air that comes through the vents will seem cool because it is room-temperature air. Turn your thermostat to “AUTO.” Now the fan will only run when the furnace is heating, and you won’t get tepid or room-temperature air.

Change the Air Filter

A dirty air filter will cause your furnace to overheat. It restricts the airflow in and out of your furnace, which can cause it to overheat. If it does overheat, the safety control will shut off the burners, causing the fan to blow cool air vs. heated air through the house.

Check the Pilot Light

Your furnace may be blowing cold air because the pilot light has gone out. It is a simple fix. Just relight the pilot. If it continues to go out after you relight it a few times, then you should call us at 512-257-8423 or request service online. This may be indicative of a bigger problem requiring professional help.

Reboot Your System

If you have a modern furnace, you probably have one that is controlled by a circuit board. Sometimes there is simply a glitch in the system, and it needs a simple reset––the same way you would restart your computer or phone. If you turn off your furnace for 30 seconds and then turn it back on, it may reset itself and begin functioning correctly. If it doesn’t start working the way it should after you have reset the circuit board, call us or request service online today.


The older your ductwork is, the more likely it is to be damaged or leaky. If you have damaged or leaky ductwork, air can be escaping before it gets to the desired living areas. Inspect the ductwork yourself, but it’s possible that you may not be able to visually detect the rips or tears causing your leak. It is best to call us or request service online for an in-depth ductwork inspection.

If none of these work, your furnace may have a bigger problem. Contact our professionals at BlueAir today to diagnose and fix any problem you might be having.

Need HVAC Service?

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Call us at 512-257-8423!

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