What Does It Mean If My Furnace Is Blowing Cold Air?

If your furnace is blowing cold air, the problem could be many things. Although your furnace could be broken, there are many other less serious problems your furnace could be having. There are many ways that you can troubleshoot your unit before it's time to call for help. 


The first thing you should check is your thermostat. This is especially important if you're living in a house with many other people, and, in particular, children. Someone may have mistakenly changed the setting on your thermostat to the attic fan, or they may have switched the fan on, which would mean that the blower would remain on even when the furnace is not heating your home.   

Gas Supply

If your furnace runs on gas and the gas supply isn't on, then the heating elements in your furnace won't work. The easiest way to check if your gas supply is on is to turn on the stove (assuming it, too, runs on gas). If the stove lights, then your gas must be on. If your stove isn't gas, then check the gas at the meter outside your house. If the valve for the meter is placed in a position that is parallel to the pipe, then the gas is on. If the valve is in a position perpendicular to the pipe, then it's been turned off.


Check that your pilot light is on. Your furnace will have instructions for turning and off the pilot light on the outer casing of the unit. Refer to the instructions to find your pilot light. If the pilot is off, follow the instructions to relight the pilot.

Air Filter

Check your air filter for dirt. If the air filter is too clogged, your system may not be getting the volume of air it needs to warm your home. This could cause the system to either produce a very low hot air output, or it could cause your heat exchanger to overheat, which would in turn cause the furnace to shut down.

Duct Leaks

Your air ducts are most likely located in your attic, where it's probably very cold right now. If your air ducts have leaks, the warm air from your ducts could be mixing with cold air from your attic, resulting in cool air blowing through the ducts. You can fix this problem by fixing the duct leaks. Use duct sealant and utility tape for small leaks. For large leaks, you may need to call a professional.

If these tips don't help, then it may be time to contact a professional. Call a reputable furnace repair person from your area. He or she can diagnose and fix your problem, and may be able to tell you how to avoid this kind of trouble in the future.