Why Is Your Furnace Blowing Cold Air?

Feb 16, 2024

Here in Winnipeg, we rely on our furnaces to keep us warm and safe through our cold, harsh winters. When your furnace is blowing cold air, you’ll want to fix it right away—below are some of the most common causes and what you can do about them: 

Your Furnace Needs To warm Up or Your Thermostat Isn’t Set Right

Furnaces can’t instantly start heating your home; air might start blowing through your vents well before it’s fully heated. We recommend waiting 10-15 minutes after you turn on your furnace to see whether or not the air heats up. You should always turn on your furnace before cold weather really starts to set in—this way, you can test to see if it works before things get too chilly.

Another common problem is a furnace that’s set to “On” instead of “Auto” (which will cause the fan to constantly blow) or a thermostat set to the wrong temperature. Check both before you continue investigating. 

Your Pilot Light Isn’t Working

Pilot lights are used in some gas furnaces—the most common type of furnace here in Winnipeg. When there’s a draft, a dirty valve, or problems with the thermocouple (which shuts off gas when there’s no pilot light detected to prevent dangerous gas buildup), you may need professional help.

Typically, pilot lights are only used on older furnaces—if your furnace is 20 years old (or older), you may need to relight your pilot light in order to get heat. When your pilot light keeps going out, call us. 

There’s a Problem With the Gas

Your furnace might start to blow cold air if there’s a problem with the gas supply—with nothing to generate heat, the fan will just circulate cold air through your house. First, check your gas valve and make sure it’s on. You can also check other gas appliances in your home to see whether or not they’re working. When the gas valve is on, but there’s no warm air coming out of your furnace, call a professional—and consider turning the gas valve off until they arrive. 

There’s a Problem With Your Air Ducts

When your ducts are clogged or leaking, there may be less warm air circulating through your home. Generally, cold air won’t blow from your vents in these cases—there’ll be little to no noticeable airflow at all. Nonetheless, if your furnace is on and you let your hand hover above your ducts, the lack of warm air might feel cold.

The answer here is simple enough: Clean up your ducts and fix any damage. Duct cleaning is usually not the priority here; we can help fix your ducts, but in the meantime, consider using duct tape to patch any obvious holes. 

The Flame Sensors Are Blocked or Damaged

Flame sensors—also called flame detectors or flame rods—are present in the modern version of furnaces (those without pilot lights). They check whether or not a furnace is burning gas. They can malfunction thanks to sediment buildup, faulty wiring, fractures, rust, corrosion, and other factors.  

When a flame rod malfunctions, your furnace may quickly cycle from blowing hot air to blowing cold air; it may also blow cold air continuously. Cleaning or replacing the flame rod can solve these issues. 

The Furnace Has Overheated

Furnaces overheat due to clogged filters, mechanical failure, and a variety of other problems. When this occurs, your furnace will shut down—and it may blow cold air for a few moments before it does. Check your air filter; if that’s not the problem, and you believe your furnace is overheating, we recommend calling the professionals.


A furnace that blows cold air isn’t much of a furnace at all. When your furnace is malfunctioning, we can help with all of the issues we’ve discussed—a gas supply that’s not working right, broken air ducts, replacing a dirty air filter, cleaning or replacing flame sensors, and more.

These are just some of the most common issues—there are other problems that can lead to a furnace blowing cold air. From problems with your furnace’s heat exchange or your furnace burners to anything else impacting the heating process, when you need furnace repair, we can help.

We’re here for furnace installation and furnace repair in Winnipeg—give us a call! 


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