Why Is My Furnace Blowing Cold Air?

Here in Chicago, we’ve spent the last few weeks with temperatures in the single digits. When it gets this cold, your heating system should be hard at work filling your home with warm air. We’ve received a number of calls from customers asking, “Why is my furnace blowing cold air?”

If you’ve noticed cold air coming through your vents when your furnace should be heating the air, there might be a quick fix.

Check Your Thermostat

Even on the coldest days, your furnace shouldn’t need to blow hot air through the vents continuously to heat your home. Once it reaches the temperature you set on your thermostat, it should stop fueling the fire until it’s needed again. However, if your thermostat fan is set to ON, it will continue to blow air through the vents.

To solve this problem, make sure your thermostat fan is set to AUTO. Doing so will prevent the fan from blowing cool air around your home when the furnace isn’t in use.

Check Your Furnace Filter

If your furnace filter is clogged, it can prevent hot air from your furnace from finding its way into your vents. Replacing a dirty air filter might be all you need to do to get the hot air flowing again.

When you locate your furnace’s filter, shine a bright light on it. If none of the light passes through, it’s time to replace the filter.

Check Your Furnace’s Pilot Light

Gas furnaces have a pilot light that needs to stay lit at all times. Furnaces rely on the pilot light to ignite the gas supply that heats your home. You’ll need to relight the pilot if it goes out for the furnace to function properly.

The furnace’s flame sensor will shut off the furnace if it doesn’t detect a flame when the gas line is open. Doing so prevents your home from filling with gas. This necessary safety feature will protect your family from inhaling dangerous gas and even potential explosions. It also allows temperatures to drop until you relight the pilot.

Relighting the Pilot Light

1. Set the pilot valve to “Off”

The pilot light assembly is usually located near the bottom of the furnace. It should have a valve with “On,” “Off,” and “Pilot” settings and a reset switch. Set the valve to “Off” to stop the flow of gas.

2. Wait five minutes

After setting the pilot valve to “Off,” wait five minutes for the gas to clear the chamber. Trying to relight the pilot with gas still in the chamber could start a fire.

3. Change knob back to “Pilot”

Once gas has cleared the chamber, spin the dial on the pilot valve back to “Pilot.”

4. Press the reset button and light the pilot

With the dial set to “Pilot,” press and hold the reset switch and light the pilot with matches or a lighter. Continue to hold the reset switch for a few moments until the pilot burns steadily.

With your pilot light burning once again, your furnace should be back in business, pumping hot air through your home. If you’ve tried each of these fixes and still notice cold air coming from your vents, it’s time to call in the pros at Blue Frost Heating & Cooling. .

Blue Frost Heating & Cooling offers furnace repair in St. Charles and throughout the West Chicago area. If your furnace is blowing cold air, don’t wait another minute in the cold. Give us a call and we’ll have one of our technicians out to get your furnace up and running in no time.

We also specialize in high-efficiency heater installation outside Chicago. So if your furnace is beyond repair or you’re looking to save money on your monthly utility bills, we can help. Call today for a free estimate.