Why is My Furnace Blowing Cold Air?

You may be tired of dealing with the cold weather already – and winter hasn’t even officially started. To make this time of year a little more bearable, you depend on your furnace to keep your home toasty and warm. There’s nothing worse than waking up in or coming home to a house that is bitterly cold. Did you leave a window open? Did the thermostat settings get changed and shut the furnace off? Or is there another problem with your heating system that needs to get taken care of?

If you put your hand over a vent and notice that it’s blowing out cold air, it’s annoying and leaves you asking, “Why?” Regardless of the cause of the problem, it’s something you need to get remedied as soon as possible so that your family doesn’t have to suffer in an uncomfortable home for very long – especially during this time of the year when the temperatures may be less than desirable.

Check out these common causes for furnaces blowing out cold air.

Thermostat issues

Before going into panic mode and thinking that you’re going to have to spend hundreds, or even thousands, of dollars on repairs (or replacement) of your furnace, check your thermostat. Someone may have accidentally adjusted the settings on the unit. If the fan setting was switched to “ON,” this means that the fan on your system will run continuously. When this happens, any pockets of cold air in your home will continue to be circulated, and your home will feel colder than it should since most of the air being circulated throughout your living space is cool.

Additionally, take into consideration whether you just had a new thermostat installed. Sometimes, homeowners choose a new thermostat that isn’t compatible with their existing heating system. When this happens, the thermostat can’t send the right signals to the heater, thus the temperature you set your unit at doesn’t really matter since the furnace won’t cycle on and off as it should.


Haven’t changed your furnace filter lately? If that’s the case, the filter is likely caked in dirt and dust. When this happens, it’s nearly impossible for air to flow properly through your heating system and this can cause the unit to overheat. Overheating can shut down the burner inside your heater, and then you’re left with a system that only can blow out cold air.

Check your filter and replace it, if necessary. If the furnace continues to blow cold air, call in a professional for assistance and diagnosis of the problem.

Pilot light has gone out

If you have a natural gas furnace, the cause of your cold home may be that the pilot light on your heating system has gone out. Sometimes, this can happen if air has blown through the area where your furnace is installed. For example, if you recently had a window near your furnace open, a gust of wind could have blown the light out. If this is the case in your home, call in a heating professional to relight it for you.

If this is a recurring problem with your gas furnace, the problem could be with the thermocouple on your unit. The thermocouple is responsible for controlling ignition and the gas valve. An issue here could mean that the pilot light continues to get extinguished.

Issues with the control panel

If you have a more modern furnace installed and notice that the system is blowing cold air, you may need to reset the control panel to get the furnace to work normally again. Most times, a furnace can be reset by shutting the system down, waiting a few seconds, and then turning the unit back on. If this doesn’t take care of the problem, call in a heating expert.

Leaking air ducts

Your ducts are responsible for transporting heated air throughout the different areas of your home. If there are “leaks” in the ducts in the form of holes or loosened panels, cool air from outside the ducts can be drawn in and mixed with the heated air on its way to your vents. If that happens, the air will not be as warm as it should be.

Protect your home’s heating system

Before a problem arises with your home’s heating system, sign up for our Heating Repair Plan so the system will be protected when it stops working like it should. Our plan includes repair coverage for one primary gas, oil, electric, or propane furnace or boiler. To learn more, visit us online.