Why Is My Furnace Blowing Cold Air?

digital temperature control

What makes our homes different from caves? If you said air quality and temperature, you are absolutely right! Furnaces are an essential part of any home, especially in colder climates. They work by heating up air and circulating it throughout the house, keeping everyone warm and comfortable. However, furnaces can sometimes have problems and start blowing cold air instead of hot. This can be extremely frustrating, especially in the middle of winter. Not only is it uncomfortable, but it can also be costly as you'll be using more energy to try to heat up your home. If you're struggling with keeping your home at a comfortable temperature, or noticing that cold air is blowing from your furnace when you turn on the heat - take a look below for some reasons why.

1: Dirty Flame Sensor

A flame sensor is a device that is used in a furnace to detect the presence of a flame. When the gas valve opens to start the combustion process, the current from the sensor moves to detect the heat from the flame. If there is no flame present, the current will not be detected and the furnace will not turn on. Flame sensors are an important safety feature in furnaces, as they prevent the furnace from turning on if there is no flame present. This can help to prevent dangerous situations, such as a build-up of gas within the furnace. Annual maintenance is one of the best ways you can prolong your equipment life. Many furnaces don’t have pilot flames anymore. Instead, they have safety devices such as these flame sensors. If your flame sensor detector is covered in dust or insulated by lint (if your furnace is located next to the dryer), you will quickly lose heat and your furnace will blow cold air. That’s why cleaning that sensor is an important part of regular maintenance

 2: Air Filter is Restricting Airflow

If you haven’t replaced your filter for some time, it becomes covered in dust and debris, which restricts the airflow to the unit. Blocked air or very poor airflow will cause overheating, which will trigger safety devices and stop the normal function of your furnace.

 3: Low Gas Supply

If your furnace is blowing cold air, it may indicate that there is an issue with the gas supply to your house. Furnaces are designed to deactivate when they are not getting enough gas. This is not something that we recommend trying to fix on your own, and it’s better to call a professional as soon as possible to prevent any possible damage or safety hazards.

 4: There’s Damage To Your Ductwork    

You may get cold air when there are holes and cracks in your ductwork, depending on their size it can allow cold air to come in from attic space. Warmed air may be escaping from those cracks and the system is working harder, making your energy bills rise – nobody wants that!

 5: The Thermostat is Set to On Instead of Auto.

The first thing you should do when cold air is blowing is to ensure the thermostat setting is correct, whenever “Fan” is set to ON position it will continuously have a blower fan running to circulate air inside your home. Even when your heat is turned off. 

If your furnace is blowing cold air, it's important to contact a professional as soon as possible to diagnose and solve the problem. Furnaces are complex systems and trying to fix them on your own can be dangerous. 


If you are experiencing any of these problems, don’t hesitate! Contact the professionals at Duct Professor Inc. Our team of experts can quickly identify the problem and get your furnace back up and running safely and efficiently. Don't suffer through a cold winter - contact us today! 

For further questions, call us at (847) 744-8099