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Carolina Climate Control Blog

Why Is My Furnace Blowing Cold Air?

Furnace problems are never welcome. A furnace that has stopped working or is blowing cold air is frustratingly inconvenient.


A lot of things can cause your furnace to behave strangely. This blog will look at some of the most common furnace problems, how you can troubleshoot them, and what you can do to fix them.



Check the Thermostat



Your thermostat determines the temperature in your home and configures your furnace to reach the desired room temperature. Sometimes your thermostat can be set incorrectly, which will cause your furnace to blow cold air.



Check to see if your thermostat is set to heat. If it’s set to cool, that may be the problem. You’ll also want to make sure that your thermostat is set to “Auto” and not “On.” The auto setting configures your fan to stop blowing when the desired temperature is reached. 



If it’s set to on, this will keep the fan running even when the furnace is off, which means it’ll be blowing cold air.



The Furnace Isn’t Warmed Up



If you notice your furnace blowing cold air, it could simply need more time to warm up. Some furnaces need upwards of 15 minutes to reach maximum potential. This could also be the case on colder days when the outside air temperature dips below 30 degrees Fahrenheit. 



Give your furnace time to warm up for at least 15 minutes. If your furnace is still blowing cold air after 15 minutes, call a professional to diagnose the problem.



The Filter Is Dirty



The air filter from your heating and cooling system will catch dust, dirt, and debris. If your air filter is clogged, it can limit airflow to your furnace, which can cause it to overheat and shut off.


Be sure to check your filter regularly for any dirt or damage. If your furnace is blowing cold air, check the furnace to see if debris are caught in it. If there are, replacing your air filter should get warm air blowing again.



Condensate Lines Are Clogged



Condensate lines move water condensation away from your furnace. If there’s water present near the igniter, it will cause an ignition failure, which could cause your furnace to blow cold air. 



Your condensate lines can clog due to mold or other debris. Make sure to drain the condensate lines. If this seems like too much for you to handle, call a professional HVAC technician and have them take a look at the problem.



Check Your Ducts for Damage



Make sure to check your ductwork. If there is damage to your ductwork, this could cause warm air to escape, which will leave some rooms with cold air. This could be due to the age of your system, which can rust over time, or it could be from small rodents or other animals chewing through the ducts.



Make sure to inspect the ducts for any holes or damage. You can seal damaged ducts with tape or replace the damaged sections.



Check the Gas Supply



If your furnace runs on gas and is blowing cold air, check the gas lines or supply. You may be running low on gas, which means the pilot light keeps going out. Or, you may have damage to the gas line that supplies your furnace. 



The good news is that if there’s a fault with the gas supply, your furnace will automatically shut off. Have a professional check the gas lines and the gas supply for any problems.



Furnace Is Overheating



Most modern furnaces have safety features to prevent severe damage or disasters from happening. If your furnace is not working correctly, it will shut down on its own. Here are the main reasons why a furnace can overheat and shut off.



Mechanical Failure



Furnaces have many moving parts in order for them to operate. If one of these moving parts fails, it can make your furnace run harder, which can ultimately cause it to overheat. If you believe your furnace is failing due to a mechanical issue, have a professional HVAC technician inspect your furnace for any problems.



Clogged Filter



A clogged filter is one of the more common furnace problems. When your air filter is clogged, your furnace will be working harder than expected. If it runs too hard, it can potentially overheat and shut down on its own. 



Preventative maintenance is critical for your furnace to run optimally. Depending on the manufacturer’s recommendations, be sure to inspect and replace your air filter every 3-6 months. Doing this can prevent thousands of dollars in repair.






Even with the best preventative maintenance schedule, your furnace can still overheat due to age-related internal failures. Age will lead to corrosion or worn parts. Over time, your furnace will need parts replaced to keep it running correctly. 



If this happens, you’ll have to ask yourself what the most cost-effective route to take is when it comes to your furnace issues. Failing internal parts in your furnace can range from a couple hundred dollars to several thousand dollars. 



If that’s the case, you may want to replace the entire furnace rather than have it repaired.


What to Do if It’s Still Blowing Cold Air



There’s nothing worse than a furnace blowing cold air on a cold night. The best thing is to look over all the tips we’ve gone over and diagnose the problem accordingly. 



Addressing these issues first will most likely solve your problems. If you’ve addressed all of these common furnace issues and you’re still having problems, you’ll need to reach out to an HVAC company and they can help. 



We specialize in all heating systems such as furnaces, heat pumps, and geothermal heating.


Give us a call and one of our technicians can help you out right away!

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