Reasons Why Your Furnace Is Blowing Cold Air

As the weather has cooled off, your furnace is working hard to keep your home comfortable. However, sometimes you may notice your heater blowing cold air. If that happens, you’ll probably want a quick solution. 

There are many possible reasons why a furnace might be blowing cold air. Keep reading to learn about some of the most common causes and what you can do to fix the problem.

Your Furnace Still Needs to Heat Up

Because a furnace has many moving parts, it takes some time to get going. So if you turn on the furnace and it starts blowing cold air, give it a little more time. This is especially true if it’s the first time you’ve used the furnace this season.

If your furnace doesn’t start blowing warm air within 15 minutes, there could be a problem with the system.

Thermostat Is Incorrectly Set

If you notice that your heater isn’t blowing hot air, check the settings on your thermostat. Although unlikely, you may have forgotten to move the switch to the ‘Heat’ position. The good thing is that this can be fixed easily within a few seconds.

To keep your furnace running efficiently, ensure the thermostat is set to ‘Auto.’ If it’s switched to ‘On,’ the fan will continue to blow air even when the unit is off, which can cause some problems. 

By setting the thermostat to ‘Auto,’ the furnace will come on simultaneously with the fan, providing the most comfortable and eco-friendly way to stay warm all winter long!

There’s No Pilot Light

If you’re feeling cold air from your furnace, check the pilot light. Many older models have a pilot light, a small blue flame used to heat the system. The furnace can’t generate heat without this light, which is probably why you’re feeling cold air.


If your furnace only blows cold air, it may be because the heater has overheated. But don’t worry, this usually doesn’t mean the unit is broken. When the system overheats, a safety feature shuts the system off. This is good—it could prevent a fire, carbon monoxide leak, or even an explosion. 

Furnace Filter Is Dirty

A clean furnace filter is crucial for an HVAC system to function properly. When the filter is clean, it allows fresh air to circulate in your home. However, when the filter is dirty, it can lead to a heater blowing cold air.

If this filter gets too clogged, it will block the airflow over the furnace’s heat exchanger. This can cause the system to overheat and trip a high-limit switch, which shuts the unit down. 

If the furnace filter looks excessively dirty, replace it. Filters should be replaced every 1-3 months depending on their size. Filters can be bought cheaply from most home stores. If needed, contact Legacy Heating and Cooling.


After reading this article, and you still aren’t sure why your furnace is blowing cold air, contacting a professional to handle the issue is essential for your home and family’s comfort. A specialized HVAC technician from Legacy Heating and Cooling can accurately assess your system and perform the necessary repairs.

If you need furnace repair, maintenance, or other HVAC services in Calgary or Edmonton, contact Legacy Heating today! Our team of experts has been helping residential clients maintain their heating systems. Get in touch with us now for more details. 

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