Why Is My Furnace Blowing Cold Air? Common Causes and Fixes For Chicago Homes
There’s nothing more frustrating than turning on your furnace in the middle of a Chicago winter—and feeling cold air blow from the vents. If your furnace is blowing cold air instead of heat, don’t panic. This common issue can stem from a number of causes, many of which are easy to fix, including:
- Thermostat Settings Are Incorrect
- Duct Issues
- Clogged Air Filter
- Furance Ignition Issue
- Furnace Is Overheating
Why Is My Furnace Blowing Cold Air?
In this post, Shavitz Heating and Air Conditioning will walk you through the most likely reasons your furnace is blowing cold air and what you can do about it.
No Heat! Check if Thermostat Settings Are Incorrect
Believe it or not, sometimes the problem isn’t with your furnace but the thermostat!
It may sound too simple, but incorrect thermostat settings are one of the most common reasons homeowners call for furnace repair. If your thermostat is set to “FAN” instead of “HEAT,” your system will blow room-temperature air regardless of the temperature set. Or if the temperature is set too low, the furnace won’t kick on at all.
A quick check of your settings could save you time, money, and a cold night under extra blankets.
What to do:
- Make sure the system is set to “HEAT,” not “FAN” or “AUTO.”
- Set the temperature higher than the current room temperature.
- Check if any smart thermostat programming is overriding your settings.
Duct Issues Might Be Letting the Warm Air Slip Away
If you’re getting a blast of cold air right when your furnace kicks on, it’s easy to assume the system just needs a minute to warm up. But here’s the thing: in a properly working furnace, the burners actually fire up before the blower turns on—so the air coming out of your vents should already be warm.
If it’s not? The issue could be hiding in your ductwork.
What could be going on:
- Leaky ducts might be pulling in cold air from unconditioned spaces like attics or basements.
- Long duct runs can let air cool down before it ever reaches your vents.
- Your blower delay might be set incorrectly, pushing air through too soon.
What to do:
Give it a moment to see if things even out—but if your vents keep blowing cold, it’s probably time to check the ductwork and system timing. A professional inspection can pinpoint the problem and get that warm air flowing properly.
Related: Why Isn’t My Furnace Heating My Entire Home?
A Clogged Air Filter Might Be Choking Your Heating System
It’s easy to forget about your air filter—but it plays a big role in your furnace’ health. When the filter gets clogged with dust, pet hair, and other debris, it can restrict airflow and make your system work even harder to keep you comfortable on those cold Chicago days than it already is.
Here’s the catch: when airflow is blocked, your furnace can overheat. And when that happens, it may shut off the burner as a safety measure, but keep the fan running—leaving you with a stream of chilly air blowing through your vents.
What to do:
Take a quick peek at your air filter. If it looks dirty or clogged, swap it out with a fresh one. Most homes need a new filter every 1–3 months, especially if you have pets or allergies.
Related: How Often Should You Replace Your HVAC Filter?
No Heat? It Might Just Be a Furnace Ignition Issue
Sometimes your furnace isn’t broken—it just can’t get the flame going.
Older furnaces rely on a small pilot light to ignite the heat; if that flame goes out, the furnace won’t produce any warmth. Newer furnace models use an electronic ignition system, and those can run into issues too—especially if a sensor is dirty or worn out.
What to do:
- If you have an older furnace, check to see if the pilot light is still lit.
- If your system keeps clicking or trying to start without success, it’s probably time to call Shavitz for a quick fix.
Related: 5 Reasons Why Regular HVAC Maintenance Is Essential
Heater Blowing Cold Air? Your Furnace Might Be Getting a Little Too Hot
Here’s something you might not expect: your furnace can overheat—it can actually shut itself down—kind of like a safety timeout. The burners turn off, but the fan keeps running to cool things down, which can feel like your system is blowing cold air.
This usually happens when airflow is blocked, causing the system to work harder than it should.
Common culprits:
- A clogged air filter
- Closed or blocked vents
- A struggling blower motor
What to do:
Start by replacing your filter and making sure nothing is blocking your vents. If that doesn’t do the trick, it’s time to call in a pro from Shavitz Heating to take a closer look.
Related: Why Won’t My Furnace Stop Running?
Still No Heat? It Might Be Time for a Service Call
If you’ve run through the quick fixes and your furnace is still giving you the cold shoulder, there could be something more serious going on behind the scenes.
Sometimes, a worn-out part—like a gas valve, a limit switch, or a heat exchanger—is keeping your system from working properly. These issues aren’t always obvious, but they can definitely stop your furnace in its tracks.
What to do:
At this point, it’s best to call a licensed HVAC technician to take a look. The trained eye of a Shavitz Heating technician can diagnose the problem quickly and safely—so you’re not left bundling up indoors.
Related: How Can I Make My Furnace Last Longer?
Don’t Let a Cold Furnace Leave You in the Cold
Cold air from your furnace doesn’t always mean disaster. From simple thermostat settings to more complex mechanical issues, there are many reasons your system might not be heating properly. With professional maintenance and timely repairs, you can keep your home warm and comfortable all winter long.
Related: What’s That Smell Coming From My Furnace?
Call Shavitz Heating Today for Furnace Repair
If your furnace is blowing cold air, Shavitz Heating & Air Conditioning can help. Our expert HVAC technicians serve the Greater Chicago area and will quickly diagnose the issue to restore warmth to your home—fast.
Call us at 847-861-5559 or request service online to schedule a heating service or inspection.