Why is my Furnace Blowing Cold Air?

There’s nothing worse than going to turn on the heat on a chilly day only to find that your furnace is blowing cold air. There are a handful of different components that could be the culprit for the cool air. Fortunately for you, correcting the issue shouldn’t be too difficult. Common issues usually surface surrounding a flame detector, gas supply, pilot light, air filter, or condensate lines. If your furnace is blowing cold air, don’t panic! Here are a few things you can do to troubleshoot the issue and get your home back to a comfortable temperature.

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Faulty Pilot Light


Why is my furnace blowing cold air? You could be dealing with a faulty pilot light. Older units are equipped with this, which is just a small flame that is necessary to light the furnace burners.

Newer units run much more efficiently and use alternative ways to light your furnace. New units will typically come with an electric igniter that creates a spark to light the burners. If you do have a furnace with a pilot light you can try to relight it.

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Inadequate Gas Supply

Something that correlates with a faulty pilot light is an issue with the gas supply. Not having the necessary gas supply will cause the pilot light to go out.

If your pilot light instantly goes out or doesn’t light at all, you might have a gas supply problem on your hands. But not to worry, furnaces are designed to turn off in these situations. If it isn’t lighting at all, it’s likely you have a gas valve problem.

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The Thermostat Is Set Incorrectly 

It might seem silly, but one of the most common contributors to furnaces blowing cold air is the thermostat not being correctly set. Thermostats can be adjusted to one of two fan settings, either on or auto.

When set to on, the furnace fan will run at all times, even when the furnace system itself isn’t running. You can put your hand up to a vent and feel the air blowing, but it won’t be heated or cooled. Switching the thermostat to auto will make your furnace fan kick in when the thermostat in your house detects a temperature different than what it’s set to.

Ductwork Issues

If there is a leak in the duct system that runs throughout your home, there’s a chance air from cooler rooms – like your basement – can enter the system, resulting in colder air coming from the vents.

Patching up any leaks in the ductwork should help to correct this problem.

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Clogged Condensate Drain Lines

Although newer high-efficiency model furnaces don’t come with pilot lights, they will have a condensate drain. It is necessary to remove any water that forms while your furnace heats the home.

Should this drain become clogged, it could prevent the furnace’s burners from lighting. The system is designed to do this – that is why it is so important to stay on top of this.

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System Overheated

Furnaces are equipped with safety components that will force your furnace to shut down to prevent overheating. There are a couple of reasons why this could happen.

Dirt and debris can build up over time and get into the furnace’s various parts, causing it to overheat. If one of the furnace’s mechanical components starts to fail, this can also lead to overheating.

Dirty Flame Sensor

A dirty flame sensor will prevent your furnace’s gas burner from staying lit. A good indication of this is if your system keeps cycling on and off.

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Air Filter is Restricting Air Flow

Restricted airflow is a huge contributor to a furnace overheating and can be caused by something as simple as a dirty air filter. As dirt builds up on the filter and is left unchecked, over time, this dirt will affect the air from passing through.

This will cause the system to run longer and work harder, which can lead to overheating. Replacing your filter ahead of every cold season is a good habit that will prevent this issue from occurring.

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The furnace isn’t Warmed up Yet


A furnace blowing cold air right when the system fires up is to be expected. Furnaces have burners that need to be ignited and then heated in order to create warm air to heat our homes.

Wait a few minutes after turning on your furnace and check to see if the temperature has improved. If after ten to fifteen minutes you notice your furnace is still blowing cold air, it’s time to call an expert.

Troubleshooting a Furnace Blowing Cold Air 


These are the typical reasons why a furnace is only blowing cold air. Whenever you have heating and cooling issues, call the professionals at Northwind HVAC for furnace and HVAC repair and installation services.

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