When it’s cold outside, the last thing you want to find is cold air coming out of your furnace when it’s supposed to be heating your home.
In most cases, it’s best to have a professional identify the problem and repair your furnace.
Here are some possible reasons your furnace is blowing cold air:
- The furnace is overheating
- You have a faulty ignition system
- The fan limit switch is broken
- Your ducts are leaky
We’ll explain what can cause these four issues in greater detail and why it’s best for a professional to handle the repair.
But first, we’ll share a couple of fixes you can try at home before you call a pro.
Before you call a pro, try these fixes:
First, check your thermostat
Make sure the thermostat’s screen is on and the buttons are responsive. If they’re not, try changing the batteries. If the thermostat isn’t responsive, call a professional.
Double-check that your thermostat is set to HEAT and not COOL. Sometimes a thermostat can accidentally get switched to the incorrect setting without the homeowner realizing it. If this is the case, we may have solved your problem.
After making sure your thermostat is set to HEAT, make sure the fan is set to AUTO and not ON. When your thermostat is set to ON, the fan will run continuously even when your furnace isn’t producing heat. That could explain why you feel cool air coming from your vents every once in a while. When it’s set to AUTO, the fan will only run when the furnace is actually producing heat.
Next, check your air filter
After you check your thermostat, it’s time to check your air filter. A dirty air filter will restrict airflow to your furnace and can cause it to overheat. If your air filter is dirty, replace it ASAP. If your furnace starts to run properly after the filter is changed, you’ve solved the problem.
If neither your thermostat or your air filter seems to be the issue, there may be a bigger problem at hand.
Cold air problems that require professional repair
While it sounds counterintuitive, an overheating furnace can actually produce cool air rather than warm air. Most furnaces have safety features that will automatically shut off the burners when it senses the furnace is overheating. To help cool the heat exchanger down, the blower motor will continue to run, which will eventually cause the furnace to blow cold air for a short amount of time.
Furnaces can overheat for a variety of reasons, including:
- Clogged vents can restrict airflow and lead to overheating. Make sure your vents aren’t being covered or blocked by any furniture or other objects.
- Dirty air filters and other components can restrict airflow. Over time, buildup of dust, dirt and other particles can clog your filters and cause your furnace to overheat.
- Short cycling occurs when a furnace turns off too soon in the heating cycle. If this happens over and over, it can put stress on the furnace’s heat exchanger and blower motor and may lead to overheating.
If you’ve already checked your air filter and you know it’s not the source of the problem, you’ll need to contact a professional for a furnace inspection..
A faulty ignition system
The type of ignition system in your furnace will depend on the furnace’s age and manufacturer. Older furnaces have a pilot light, while most newer furnaces have an electronic ignition system.
With electronic ignition systems, cold air could be caused by an electrical issue or if parts need to be adjusted or replaced. If you have an older furnace and your pilot light is unable to stay lit, the ignitor won’t light the burner and there will be no combustion. Without combustion, you won’t have heat.
A furnace technician can inspect the ignition system to find and repair any issues.
Broken fan limit switch
Your furnace’s fan is controlled by a limit switch which tells it when to turn on and off. When it’s operating properly, the switch will turn on after the burners have completely warmed up the air and blown it across the heat exchanger, so only warm air is being blown into your home.
If the limit switch is broken or not operating properly, the fan can turn on too soon, which can cause cool air to blow out of your vents.
A professional can check the limit switch to make sure it’s working correctly. If it’s not, they can replace it.
Leaky air ducts
If you have leaks or holes in your air ducts, warm air can easily escape which could explain why you’re feeling cool air coming from your furnace instead of heat.
Leaky air ducts can also make your furnace work harder as it strives to meet your desired temperature that’s set on your thermostat.
Unfortunately, this is not a problem you can fix on your own. Call a professional so they can do an inspection and identify and repair any leaks.