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Why is My Furnace Blowing Cold Air?

October 29, 2021 | Blog

There’s nothing worse than when winter rolls around and you rush to turn on your furnace, only to find it blowing cold air. Big Mountain Heating & Air would be happy to help you in this situation, but there are a few things you can try yourself before you call in the professionals. Keep reading to learn more about how to troubleshoot your furnace and how to prevent furnace problems from happening. 

Thermostat settings

The first (and easiest) thing you can do is check your thermostat’s settings. If you’ve noticed your furnace blowing cool air sometimes and warm air other times, it could mean your thermostat is set to ON instead of AUTO. When your thermostat is set to ON, this means your furnace’s fans are running non-stop, even if the air hasn’t been warmed yet. 

To fix this, just change your thermostat’s settings to AUTO. Your furnace should then only run the fan during heating cycles.

Furnace air filter

If you haven’t had furnace maintenance done in a while, there’s a chance its air filters have gotten dirty. A dirty air filter is one of the most common reasons furnaces overheat and start blowing cold air as a result. The buildup of debris hinders airflow, which can cause a furnace to overwork due to the lack of heat. When this happens, your furnace’s limit switch will shut off the burners completely to prevent a fire, but the fans will continue blowing air to cool down the furnace. Cool air will then be pushed throughout your home rather than warm air. 

Before you call for furnace repair, find the filter compartment of your furnace and replace the dirty filter. Make sure you choose a replacement with the same dimensions and position it correctly when inserting. If you’re unsure about what air filter to buy or how to replace it, find the make and model of your HVAC system and contact Big Mountain Air for assistance. 

Pilot light

If your home has an older gas furnace, then another cause for cool air could be an extinguished pilot light. According to the International Association of Certified Home Inspectors, a pilot light is defined as “a small flame that is kept alight constantly in order to serve as an ignition source for a gas burner.” If your pilot light goes out, then the fuel for your furnace is not being burned, which means no heat. Your fans will still work, however, so air will go through your vents without being heated beforehand. 

If you’ve noticed that your furnace’s pilot light isn’t lit, you can try to relight it yourself. Since not every furnace is made the same, the best thing you can do is follow your model’s manual. It will give you step-by-step instructions on how to ignite a pilot light specific to your model. If you can’t find the manual, or your pilot light keeps going out, contact a technician to look into the issue further.

Another solution you could consider is a furnace replacement. Older gas models waste a lot of gas and energy to keep the pilot light constantly lit. Many modern models do not require a pilot light and could help lower your energy bill in the long run.

Call the professionals!

If troubleshooting the problem on your own didn’t work out, and you’re located in the Sacramento area, Big Mountain Air is ready to help. Whether your furnace is blowing cool air, you need a full furnace replacement or you are looking to schedule furnace maintenance, our technicians have the necessary experience and skill to keep your heating system running efficiently. Contact us today!

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What Our Customers Have To Say

Good Rebates

This is a review for a complete HVAC system replacement from Big Mountain. I started at the SMUD website looking for the best rebate program and found a list of contractors there. I vetted out companies that had a lower number of completed jobs per the SMUD rebate program data.

Lee S.

Very Professional

Had my A/C go out yesterday, called Big Mountain today and they had a serviceman in my area of Lincoln, he was here within a half hour and fix my unit in a very professional manner, and the cost was reasonable. I was very impressed with the company and the serviceman.

Tom D.


I had a appointment with them between 1-3 and one of their staff members called me and kept me updated when they will arrive which was nice. Steve arrived on time and was really nice for explaining what could the cause be. My ac fan was working but cool air wasn’t coming out.

Krystal L.