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Why Is Your Furnace Blowing Cold Air?

furnace blowing cold air

Who turned on the AC? When the weather turns and it’s time to heat your home, the last thing you want is for your furnace to blow cold air! What causes this, and what can you do about it? Let’s find out so you can take off the parka, hats, and gloves inside the house.

Troubleshooting Furnace Problems

A few different issues can cause your furnace to blow cool/cold air:

Your Air Filter is Dirty

Your furnace may blow nice hot air for a while, and then cold, then…nothing. A likely culprit: your air filter.

Air filters are designed to protect the blower fan from dust, dander, hair, etc. As a bonus, they also help filter airborne contaminants and improve indoor air quality. Over time, filters accumulate a great deal of gunk. This blocks airflow over the heat exchange, which can cause it to overheat. When this happens, it trips a high limit switch (a safety device), and your burners shut down so the heat exchanger doesn’t crack. The blower keeps working to cool the furnace.

If overheating occurs repeatedly, it can damage your very pricey heat exchanger. The good news is that replacing air filters is quick, easy, and inexpensive. Take a look at your current filter to get the correct model numbers and go to the home improvement or hardware store for a replacement.

Turn off your furnace at the thermostat and pop the new filter in. You’ll want to do this at least every two to three months, or more if you have pets. If you need help, the Mountain Air Mechanical team is happy to show you how to do it.

Still blowing cold air after you change the filter? You may need to have a technician reset the furnace .

The Thermostat Is Set to “On”

If you tell a heating technician that your furnace is blowing cold air, the first place they’ll look is the thermostat . If your fan is set to “On,” the blower runs constantly, even if it’s not heating your home. A quick switch to “AUTO” ensures the blowers only operate when the furnace is heating the air . No more cold breeze!

Your Pilot Light is Out

The pilot light is a small flame that burns continuously. It ignites the burners during the heating cycle. Most newer furnace systems do not have a pilot light; they have an electric ignition. If yours is an older model, though, and it’s blowing cold air, this could be the source of the problem.

If you take a look at your pilot light, you should see a strong blue flame. You’ll also see a copper rod which is enveloped by the flame. This is called the thermocouple. Its job is to shut off the gas going to the pilot light if the flame goes out. Without this safety mechanism, the gas could make its way into your home and create a significant safety hazard.

When the pilot light goes out, it could be because you have an issue with the thermocouple. It may be broken (shutting off the gas even if the pilot light is functioning normally), you may have soot buildup or the pilot may not be hitting the top of the thermocouple.

You can try to relight the pilot; if it stays lit, good! You can also try carefully brushing off the thermocouple if there’s soot buildup. If there is another issue, or you are not comfortable poking around with gas and flame, call your HVAC company. They’ll send a tech right over. You don’t want to be without heat this winter — and you don’t want to damage important system and safety components.

If, after troubleshooting, your furnace is still blowing cold air — or again, if you’re not comfortable with any aspect of it — don’t hesitate to call the folks at Mountain Air Mechanical . Our experienced techs will ensure you’re warm and cozy in no time .