6 Common Reasons Why Your Furnace Is Blowing Cold Air

If you’ve noticed that your furnace isn’t working properly, then you’ll want to address this issue immediately. Before you can do anything about it, you’ll need to figure out what’s wrong with the furnace. This is easier said than done as there are a multitude of things that could be wrong. To help narrow things down, we thought it would be useful to put together a brief article on this subject. If this is something that you want to learn more about, read on for the six most common reasons why your furnace is blowing cold air.

The Thermostat Is Set to “On” Instead of “Auto”

Before you start checking on the different components of your furnace, it would be good to check on your thermostat. Sometimes the issue isn’t complicated and can be addressed rather quickly. If your heater is blowing cold air, we recommend checking the temperature controls in your home to make sure the thermostat is switched to automatic mode. This will make sure that your furnace will only run during the standard heating process, not all day long without producing heat. We carry Google Nest Thermostats, Ecobee Thermostats, and Honeywell Thermostats!

The Pilot Light Is Faulty

If your furnace is not working, you’ll need to check the gas pilot light to ensure that it’s working. Older gas furnaces require light on the pilot to ignite the burners. To relight the pilot, refer to the instruction manual that came with your furnace. You can also contact Legacy Heating and we’d be happy to help!

The Gas Supply In Your Home Is Low

One of the most common reasons why your furnace isn’t working properly is your home’s gas supply. If your heater is blowing cold air, this may indicate a problem with your gas supply line. Because your furnace is designed to deactivate if it’s not getting enough gas, the issue can’t be fixed by troubleshooting on your own. We recommend calling the professional HVAC experts at Legacy Heating for assistance.

The Furnace Lines Are Clogged

Have you noticed your furnace has stopped working in your home? The newest, most advanced furnaces are engineered with a condensate drain line that removes moisture from the furnace. If there is a blockage in the line, this may cause the burners in the furnace to shut off, which may lead the furnace to blow cold air into your home.

The Ductwork Is Damaged

You may have a furnace blowing cold air through your vents due to holes and cracks in the ductwork. The holes and cracks allow cold air from your attic to enter the air ducts before your furnace can warm it. You may have a working furnace, but it is losing heat as soon as it leaves the furnace. Duct sealing may keep the warm air going towards the vents.

The Air Filter Is Restricting Airflow

If your furnace’s air filter has accumulated a coating of dust, grime, or soot, this will block incoming air from your gas furnace, and the gas furnace will overheat. Common signs of dirty air filters include long heating cycles and overheating issues. You can fix this issue by replacing the dirty filter with a new one. This will restore the flow of warm air through your house.


We hope this article proves to be useful when it comes to helping you fix any issues that you may be having with your furnace. While furnace issues may seem intimidating, they can be rather easy to address as long as you know what you are doing. If the issue persists, it may be best to reach out to your local heating and air conditioning company.

Legacy Heating is the go-to option when it comes to heating and air conditioning in Calgary and Edmonton. Looking for basement development in Edmonton or Calgary, we are here to help! We specialize in residential new home construction and installation and replacement of HVAC systems and other parts. We also have HVAC products. Contact us today!

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