woman sitting in front of furnace

Why is My Heat Blowing Out Cold Air?

Woman sitting in front of furnace

It’s fifty degrees outside and your feet are chilly. You turn on the heat only to realize your heater is blowing out cold air! Oddly enough, this is a common problem and there are several causes from the thermostat to a dirty air filter.  Here at MTB Mechanical we get these calls often and recommend taking these steps.

Check the Thermostat

First, double check to make sure you’ve turned on the heat and set the thermostat higher than the actual temperature of your home. (It happens.) Next, make sure your thermostat is set to “auto” rather than “on.” When the thermostat is set to “on,” the fan on your furnace will blow continually, even when the furnace isn’t actually heating the air. After you’ve done that, notice whether or not your thermostat is working correctly. Some thermostats run off central power with a battery backup, but what some people don’t realize is there are some thermostats that use battery power only, so check your thermostat and replace your batteries regularly.

Change the Air Filter

A dirty air filter can restrict airflow into your furnace, meaning the furnace will run longer and work harder to provide adequate heat. In addition, restricted airflow can overheat your furnace, causing a safety control to shut off the burners. However, the fan will keep running, cooling the furnace to protect it from potential damage. It’s best to change your air filters regularly, but if you need a nudge, sign up for a monthly or quarterly reminder.

Check the Pilot Light

Sometimes heating systems blow cold air because the pilot light isn’t working. Older heating systems use a standing pilot light as the source of ignition for the furnace, which is inefficient. Newer models use an electronic ignition which shouldn’t need relighting. Basically, in an older heating system if the pilot light is out, the furnace isn’t lighting the fuel, meaning it can’t heat your home, either. If you have an older model furnace, you’ll need to check for instructions on how to ignite your model’s pilot light. These instructions should be on the unit itself or in the user’s manual.


If you’ve followed all these steps and your heat is still blowing cold air, it may be from other causes, including:

  • No fuel – If you have a gas or oil furnace, your system may not be getting the fuel it needs to operate efficiently. A technician can check your pilot light to ensure it’s on, then make sure the gas or oil is flowing smoothly.
  • Shorted Components – If you have a relatively new heating system, some of its electrical components may have gone out. A professional can determine which parts need fixing and which should be replaced.
  • Clogged condensate drain lines – New, high-efficiency furnaces have condensate drain lines. Basically, this removes water that is created during the heating process. If the line gets clogged, it can activate a switch that prevents the burners from lighting.
  • Leaky Ductwork – If your ductwork has become disconnected or a duct has sprung a “leak,” cold air could be getting in and then circulating through your HVAC system. The attic is the first place to look for this kind of problem.


Lastly,there’s a possibility that your heater blowing cold air is simply a sign it’s time to invest in a new heating system. Most heaters are graded to last anywhere from 10-12 years, but use, wear-and-tear and other factors can play a role. If you have to replace your system, remember to have it serviced regularly.

If these steps don’t do the trick, you’ll want to call a professional HVAC technician. MTB Mechanical understands that when you need heat, you need it now, and we’re ready for your call 24/7. Schedule an appointment online or call 704-321-9250 today.